GIFT   OF 

j-xXS^X     C  f  1 


BIOLOGY 
LIBRARY 


THE  PLANT, 


Illustration 


OEGANIC  LIFE  OF  THE  ANIMAL. 


BY 

HARLAND    COULTAS, 

AUTHOR  OF  "THE  PRINCIPLES  OF  BOTANY  AS  EXEMPLIFIED  IN  THE  CRYPTOQAMIA, 
ETC.,  ETC. 


PHILADELPHIA: 
PERKY   AND   ERETY,  PUBLISHERS, 

S.  W.  CORNER  FOURTH  AND  RACE  STSr 

1850. 


BIOLOGY 


Entered  according  to  the  Act  of  Congress,  in  the  year  1855,  by 

HARLAND    COULTAS, 

in  the  Office  of  the  Clerk  of  the  District  Court  of  the  United  States, 
in  and  for  the  Eastern  District  of  Pennsylvania. 


PRINTED  BY  HENRY  B.  ASHMEAD, 
GEORGE  ST.  AB.  ELEVENTH. 


TO 


SAMUEL  JACKSON,  M.  D., 

PROFESSOR  OP  THE  INSTITUTES  OF  MEDICINE  IN  THE  UNIVERSITY  OF 
PENNSYLVANIA. 

DEAR  SIR, — 

Knowing  the  enlarged  and  liberal  views  which  you''  take  of 
medical  education,  and  your  willingness  to  encourage  your  stu- 
dents in  all  inquiries  tending  to  render  them  skilled  and  accom- 
plished in  their  profession, — allow  me  to  lay  before  you  this  humble 
attempt  to  show  the  uniformity  of  the  organic  laws  in  plants  and 
animals. 

I  remain, 

With  sentiments  of  respect, 
Yours  truly, 

HARLAND  COULTAS. 


284310 


CONTENTS. 


INTRODUCTION. 
GENERAL  CONSIDERATIONS  ON  ANIMAL  AND  VEGETABLE 

LIFE,         - ---13 

PART   I, 
HISTOLOGY  OF  PLANTS  AND  ANIMALS. 

CHAPTER  I. 

ON  THE  INDIVIDUALITY  OF  THE  CELLS,      -      .;-        -        -    31 
On  the  Chemical  Composition  of  the  Vegetable 
and  Animal  Tissues,  -        -        -        -        -    47 

CHAPTER  II. 

ON  THE  DEVELOPMENT  AND  PROPAGATION  OF  CELLS,  -  51 

1.  Formation  of  Cells  from  Nuclei,         -        -  -  51 

2.  Formation  of  Cells  by  Division,         - .    .    »  -  55 

3.  Formation  of  Cells  by  Gemmation,    -        -  -  59 

CHAPTER  III. 

ON  THE  TRANSFORMATION  OF  CELLS  INTO  TISSUES,     -        -    62 

CHAPTER  IV. 

Ox  THE  CONTRACTILITY  OF  THE  TISSUES,   -        -        -        -    73 


i  CONTENTS. 

PART    II, 

NUTRITION  IN  PLANTS  AND  ANIMALS. 

CHAPTER  Y. 

ON  THE  ABSORPTION  AND  CIRCULATION  OF  FOOD  IN  PLANTS 

AND  ANIMALS,   --------85 

CHAPTER  VI. 

ON  THE  NlJTRITIYE  PROCESSES  OF  RESPIRATION  AND  AsSIM- 

1LATION,  ________    104 

PART    111. 

REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

CHAPTER  VII. 

GENERAL  CONSIDERATIONS  ON  REPRODUCTION  IN  PLANTS 

AND  ANIMALS, 123 

Hybridization, 131 

CHAPTER  VIII. 

ON  THE  ESSENTIAL  AND  CONSECUTIVE  PHENOMENA  OF  RE- 
PRODUCTION,     ----____  135 

PART    IV. 

ON  THE  GEOGRAPHICAL  DISTRIBUTION  0?  PLANTS 
AND  ANIMALS. 

CHAPTER  IX. 

ON  THE  LAWS,  ACCORDING  TO  WHICH  PLANTS  AND  ANIMALS 

ARE  DISTRIBUTED  ON  THE  SURFACE  OF  THE  GLOBE,      -  153 

CHAPTER  X. 

ON  THE  GEOLOGICAL  SUCCESSION  OF  PLANTS  AND  ANIMALS, 

OR  THEIR  DISTRIBUTION  IN  TIME,        -  -168 


' 


PREFACE. 


THE  two  volumes  on  Cryptogamous  and  Phanerogamous 
plants  already  published  by  the  author,  were  written  with  an 
"  especial  reference  to  the  wants  of  medical  students  and  phy- 
sicians." Botany  has  not  yet  obtained  that  position  to  which 
it  is  deservedly  entitled,  as  a  preparatory  study  to  the  organo- 
graphy  and  physiology  of  animals.  It  is  still  excluded  from 
the  most  important  medical  schools  ;  and  this  state  of  things 
will  continue  despite  of  all  the  efforts  of  botanists,  so  long  as 
the  plant  is  regarded  as  if  it  were  isolated  from  the  rest  of 
organic  nature. 

The  functions  of  animal  life  appear  to  be  gradually  super- 
added  to  those  which  are  strictly  vegetative.  As  we  pass 
from  the  plant  through  the  coral  and  sponge  to  the  higher 
order  of  animals,  bones,  blood-vessels  and  nerves,  gradually 
appear ;  the  organs  of  the  senses  become  more  perfect,  and  the 
motions  more  complicated,  until  at  length  in  man,  the  nervo- 
muscular  system,  which  has  thus  been  gradually,  superadded 
to  the  vegetative,  manifests  itself  most  perfectly  in  all  that 
infinite  variety  of  movement  and  sensation  peculiar  to  rational 
beings.  On  the  other  hand,  as  we  descend  from  man  to  ani- 
mals still  lower  in  the  scale  of  creation,  in  proportion  as  the 


-8  PREFACE. 

functions  of  animal  life  are  suppressed,  the  vegetative  life  of 
the  organism  gradually  predominates,  until  life  becomes  wholly 
vegetative. 

Life  in  plants  is  therefore  limited  to  the  two  functions  of 
"nutrition  and  reproduction  ;  and  nutrition  and  reproduction  in 
animals  are  necessarily  illustrated  by  the  flowers  and  forest 
trees  with  which  the  earth  is  beautified  and  adorned.  Such 
appears  to  me  to  be  the  way  in  which  organic  nature  ought 
to  be  regarded,  such  the  relative  positions  of  the  vegetable 
and  animal  creation. 

Few,  we  believe,  recognize  as  they  ought  to  do,  the  benefits 
which  have  already  resulted  to  animal  physiology  and  the 
science  of  medicine,  from  the  study  of  a  few  humble  plants, 
The  great  cell-doctrine  of  physiology,  which  is  now  admitted 
to  be  the  basis  of  all  sound  scientific  investigations  into  the 
phenomena  of  organized  beings,  originated  in  the  study  of 
vegetable  matter.  M.  Mirbel,  in  a  most  admirable  memoir  on 
the  development  of  Marchantia  polymorpha,  a  little  acotyle- 
donous  plant  belonging  to.  the  family  of  the  Hepaticae,  was 
the  first  to  show  the  cellular  origin  of  every  other  form  of 
vegetable  tissue.  He  proved  that  the  fibre  cells  of  plants  are 
only  attenuated  utricles,  and  that  the  different  varieties  of 
vasiform  tissue  and  ducts,  by  which  the  interior  of  the  plant 
is  aerated,  originate  in  a  row  of  utricles  ;  these  gradually  elon- 
gate, and  the  various  secondary  deposits  characteristic  of  the 
different  forms  of  spiral  vessels,  appear  on  their  internal  sur- 
face ;  the  septa  or  partition  walls  between  the  several  cellules 
are  then  absorbed,  and  the  transformation  of  the  utricles  into 
vessels  is  completed.  These  observations  were  confirmed  by 
the  researches  of  Schleiden  and  other  distinguished  botanists, 


PREFACE.  9 

and  thus  a  flood  of  light  was  thrown  on  the  organization  of 
plants. 

But  how  do  the  cells  of  plants  and  animals  originate  ?  How 
do  they  multiply  and  extend  themselves  so  as  to  produce  the 
growth  or  enlargement  of  the  organs  ?  These  are  difficult  but 
interesting  questions,  and  botanical  researches  have  enabled 
us  to  reply  to  them  satisfactorily. 

A  German  naturalist,  Mohl,  selected  for  observation  one  of 
the  fresh  water  algae,  which  had  been  previously  figured  and 
described  as  Conferva  glomerata.  This  simple,  thread-like 
plant  was  placed  beneath  the  microscope,  and  the  develop- 
ment of  the  row  of  utricles  of  which  its  entire  organization 
consists,  watched.  Very  soon,  Mohl  observed  that  the  inte- 
rior face  of  the  cavity  of  one  of  the  utricles  presented  towards 
its  middle  part  a  fold,  which  increased  almost  imperceptibly 
until  it  ended  by  forming  a  complete  wall  dividing  the  cavity 
of  the  utricle  into  two  parts.  Each  of  these  then  dilated  itself 
into  a  new  utricle.  Thus  in  the  place  of  one  cell  there  were 
two  cells,  which  again  divided  in  the  same  way,  and  so  on.  It 
is  in  this  way  that  a  single  cell  gives  rise  to  a  row  of  connect- 
ed cells,  when  the  division  takes  place  in  one  direction,  and  to 
a  plane  or  solid  mass  when  it  takes  place  in  two  or  more  di- 
rections. There  are  other  modes  of  increase  which  we  shall 
notice  in  the  ensuing  pages ;  suffice  it  for  the  present  to  say, 
that  their  discovery  originated  in  the  investigation  of  crypto- 
gamous  plants  of  extreme  simplicity  of  organization. 

Up  to  this  period  it  was  believed  .by  the  most  eminent  phy- 
siologists, that  animal  and  vegetable  tissues  differed  widely  in 
their  development,  and  that  cells  existed  only  in  plants.  Such 
was  the  condition  of  things  in  1838,  when  Schwann,  taking  up 


10  PREFACE. 

the  beautiful  investigations  that  Schleiden  had  just  published 
upon  the  structure  and  growth  of  vegetable  cells,  came  to  the 
conclusion  that  animal  tissue  consisted  equally  of  cells,  and 
that  whatever  may  be  the  character  of  the  tissues^  whether 
they  assume  the  form  of  muscle,  bone,  or  blood-vessels,  all  ori- 
ginate in  cells,  of  which  they  are  but  modifications. 

Let  it  be  remembered  that  these  grand  discoveries,  which 
have  given  such  an  impulse  to  animal  physiology  within  the 
last  twenty  years,  originated  in  botanical  investigations.  After 
such  fruits  have  been  reaped,  the  study  of  the  physiology  of 
plants  ought  to  be  encouraged.  Where  would  have  been  our 
knowledge  of  the  histology  of  animals,  but  for  the  botanical 
researches  of  Mohl,  Schleiden,  Mirbel  and  other  distinguished 
physiologists?  Incalculable,  then,  has  been  the  amount  of 
good  which  has  resulted  to  animal  physiology,  from  the  study 
of  the  simple  and  beautiful  organization  of  plants,  and  in  the 
face  of  these  facts,  there  is  no  excuse  for  the  coldness  and  ne- 
glect with  which  this  department  of  Natural  History  still  con- 
tinues to  be  treated.  It  is  not  the  mere  collecting  of  species, 
the  technical  description  of  their  several  peculiarities,  and 
their  proper  classification  and  arrangement  which  is  here  ad- 
vocated, so  much  as  the  study  of  their  vital  phenomena  and 
the  laws  of  their  development.  No  extensive  acquaintance, 
either  with  rare  exotics  or  the  choicer  native  species,  is  at  all 
necessary  for  such  researches,  for  these  laws  may  be  studied 
in  the  commonest  weeds  growing  around  our  dwellings. 

The  views  on  vegetable  respiration  in  this  work  are  jiot  my 
own  peculiarities  ;  for  they  were  held  by  Dr.  Gilbert  Burnett, 
an  eminent  English  physician  and  physiologist.  I  have  also 
been  very  favorably  impressed  with  the  opinions  advanced  by 


PREFACE.  11 

Dr.  Draper,  in  reference  to  the  exciting  causes  of  the  motion 
of  the  nutritive  fluids  in  the  organism  of  plants  and  animals, 
notwithstanding  the  attempts  which  have  been  made  to  con- 
trovert them.  Let  it  be  considered  that  there  is  the  same  suc- 
cessive degrees  of  attenuation  in  the  conduits  of  both  the  sap 
and  blood,  resulting  fro'm  lateral  ramifications ;  the  same  beau- 
tiful anastomoses  amongst  the  capillaries  in  which  these  con- 
duits finally  terminate.  By  these  means  the  nutritive  fluids 
are  diffused  in  all  directions,  and  brought  into  immediate  com- 
munication with  the  cellular  tissue  of  the  organs.  Let  the 
structure  of  any  exogenous  leaf  be  examined  even  superficially, 
without  the  microscope.  The  successive  attenuations  of  the 
fibrous  system  by  lateral  ramifications  into  a  network  of  capil- 
laries, which  develop  horizontally  in  a  series  of  closely  approx- 
imated planes,  through  the  parenchyma  of  the  leaf,  show  that 
the  same  laws  predominate  in  the  distribution  and  elaboration 
of  fluids  in  vegetable  as  in  animal  matter.  At  least  it  is  not 
unphilosophical  to  infer  some  analogy,  if  not  absolute  identity 
of  function,  where  there  is  so  manifest  a  similarity  in  organic 
structure. 

I  cannot  conclude  my  Preface  without  acknowledging  my 
obligations  to  my  numerous  friends  and  patrons  through  whose 
assistance  I  have  been  enabled  to  produce  this  volume. 

In  the  preparation  of  Part  I.  an  excellent  Chevalier  micro- 
scope was  employed.  This  instrument  was  kindly  lent  me  by 
Dr.  Francis  Lewis.  It  gives  me  pleasure  also  to  mention  the 
services  of  Dr.  Samuel  Jackson,  Dr.  Samuel  Lewis,  Dr.  Francis 
West,  Dr.  S.  Tucker,  the  Hon.  W.  D.  Kelly,  and  Professor 
Saunders  of  the  French  Collegiate  Institute,  West  Philadelphia. 


INTRODUCTION. 


GENERAL   CONSIDERATIONS   ON  ANIMAL  AND  VEGETABLE 
*  LIFE. 

IF  we  cast  a  glance  at  the  immense  quantity  of  animals 
and  plants  which  live  on  the  surface  of  our  globe,  we  are 
at  first  struck  with  the  variety  of  forms  under  which  they 
present  themselves,  with  their  colors  so  diversified  and 
sometimes  so  brilliant,  and  with  the  collossal  proportions 
of  some,  as  compared  with  the  diminutiveness  of  others. 
But  when,  after  this  superficial  examination,  we  study 
them  more  attentively ;  when  we  examine  with  care  the 
structure  of  each  being,  we  at  once  see  the  perfection 
which  exists  in  its  organs,  and  how  well  they  are  adapted 
to  its  peculiar  habits  and  mode  of  life — from  the  enor- 
mous whale,  which  requires  an  ocean  to  swim  in,  to 
those  minute  and  myriad  forms  which  find  ample  room 
for  all  their  evolutions  in  a  single  drop  of  its  waters; 
from  the  lofty  tree  which  has  stood  for  centuries,  an 
ornament  in  the  midst  of  the  landscape,  to  the  lowly 
flower  which  attracts  us  by  its  beauty  and  fragrance — all 
form  a  collection  of  objects  whose  framework  is  constructed 
in  the  most  admirable  manner,  and  whose  vital  manifesta- 
tions are  in  the  highest  degree  instructive  and  interesting. 

At  first  sight,  nothing  would  seem  to  be  more  widely 


14  INTRODUCTION. 

different  from  each  other,  than  an  animal  and  a  plant. 
How  different  is  the  tree  from  the  bird  singing  on  its 
branches,  or  the  traveller  resting  beneath  its  shade.  In 
the  one  instance,  the  organism  is  immovably  fixed  to  the 
soil  which  gave  it  birth,  and  has  neither  the  faculty  of 
moving  itself,  nor  that  of  manifesting  pleasure  or  pain. 
The  hatchet  penetrates  its  tissues,  and  it  falls  without  any 
external  signs  of  suffering.  But  in  the  other  cases,  the 
organic  beings  are  far  more  highly  complicated.  They  are 
endowed  with  the  power  of  moving  from  place  to  place,  have 
a  will  and  desires,  senses  to  apprise  them  of  the  character 
and  qualities  of  external  bodies,  and  introduce  food  into 
their  interior,  where  a  special  cavity  is  provided  for  its 
elaboration  before  it  is  employed  in  the  nutrition  of  their 
organism.  Plants  have  no  such  special  receptacle  in  their 
interior.  They  live,  as  it  were,  in  the  midst  of  their  food. 
It  is  furnished  to  them  by  nature  in  a  condition  fit  for  assi- 
milation and  circulation.  They  draw  it  at  once  from  the 
earth  by  their  roots,  and  from  the  atmosphere  by  their 
leaves.  They  therefore  possess  no  special  organs  for  its 
preparation.  It  would  seem  impossible  that  there  could 
be  anything  in  common  between  bodies  so  strikingly  dis- 
similar in  their  organization  and  habits. 

But  if  we  consider  the  vital  phenomena  manifested  by 
animals  and  plants,  we  shall  very  soon  see  that  there  is 
abundant  reason  for  believing  that  the  difference  between 
these  organic  productions  of  nature  is  not  so  great  as  we 
at  first  thought. 

In  the  first  place,  both  the  animal  and  plant  spring  in- 
variably from  a  being  perfectly  similar  to  themselves,  to 
which  they  adhere  during  a  space  of  time  more  or  less 
long,  and  from  which  they  are  finally  separated  at  a  deter- 
minate epoch,  under  the  form  of  an  egg  or  .a  seed,  which, 


INTRODUCTION.  ,15 

under  envelopes  more  or  less  resisting,  encloses  a  germ. 
In  this  germ,  all  the  organs  of  the  adult  animal  and  plant 
exist  in  a  rudimentary  undeveloped  condition.  Germina- 
tion, or  the  act  by  which  these  organs  disengage  themselves 
from  their  envelopes,  does  not  increase  their  number,  but 
only  augments  their  size  or  modifies  their  form.  The  seed 
contains  the  plant,  and  the  egg  the  animal.  Thus,  they 
are  alike  at  the  commencement  of  their  being.  In  the 
second  place,  the  organs  of  plants  and  animals, — the  root, 
stem,  and  leaves  of  the  former,  the  bones,  muscles,  and 
limbs  of  the  latter, — will  not  grow  without  a  plentiful  sup- 
ply of  food  and  air.  In  both  instances  it  is  absolutely 
necessary  that  the  nutritive  aliment  should  be  introduced 
into  the  interior  of  the  plant  or  the  animal,  and  be  dis- 
tributed to  all  the  parts  of  their  organization.  Now  the 
absorption,  circulation,  and  assimilation  of  food  and  air,  by 
animals  and  plants,  is  in  principle  precisely  the  same 
process.  Abundant  proof  of  this  position  will  be  given 
in  the  succeeding  pages. 

Well-marked  and  obvious  distinctions  between  animals 
and  plants  exist  only  in  the  more  highly  organized  forms 
of  animal  and  vegetable  life.  As  we  descend  to  beings  of 
a  lower  rank  in  creation,  these  distinctions  become  gra- 
dually effaced,  and  we  see  successively  disappear  the  most 
important  organs  of  animal  life.  The  organs  of  the  senses 
become  rudimentary,  bones,  blood  vessels,  and  nerves  to- 
tally disappear,  and  in  proportion  as  the  powers  of  animal 
life  are  suppressed,  those  which  are  truly  vegetative  gain 
the  ascendancy.  Thus,  the  lower  orders  of  the  cold- 
blooded vertebrata,  whose  bodily  temperature  is  regulated 
by  that  of  the  medium  in  which  they  live,  become  torpid 
and  inactive  in  common  with  plants  in  winter.  So  also 
many  vertebrated  and  crustaceous  animals  change  their 


16,  INTRODUCTION. 

epidermal  appendages.  The  serpent  casts  its  skin,  the 
bird  its  feathers,  crabs  and  lobsters  their  claws,  just  as  the 
leaves  and  bark  fall  from  the  branches  and  stems  of  trees. 
Moreover,  the  exercise  of  the  reproductive  function  which 
in  man  is  not  limited  to  any  particular  time,  is  periodical 
in  inferior  animals,  precisely  as  plants  flower  and  fruit  at 
certain  seasons  of  the  year.  At  length,  in  the  lowest 
orders  of  the  animal  creation,  the  animal  and  plant  ap- 
proach each  other  so  closely  that  it  is  hardly  possible  to 
draw  any  line  of  demarcation  between  them. 

This  is  the  case,  for  example,  with  that  order  of  animals 
which  have  been  very  properly  called  by  naturalists,  zo- 
ophytes, of  which  the  coral  and  the  sponge  are  familiar 
examples.  These  creatures,  which  show  undoubted  signs 
of  animality,  present  also  at  the  same  time  many  striking 

Fig.  1. 


Fig.  1.  Hydra,  or  polype  attached  to  a  piece  of  stick,  with  its  arms  extended 
in  quest  of  prey.  a.  The  mouth  of  the  animal,  surrounded  by  the  tentacula. 
&.  The  tendril-like  grasp  of  an  aquatic  insect,  c.  Foot  or  base  of  the  animal 
with  its  suctorial  disc.  The  figure  shows  also  the  natural  size  of  the  animal. 


INTRODUCTION.  17 

indications  of  a  vegetable  nature.  They  are  not  only  fixed 
to  the  ground  like  plants,  but  they  have  also  a  plant-like 
method  of  growing  and  propagating. 

It  is  extremely  difficult  to  convey  any  general  idea  of  a 
zoophyte,  because  there  is  no  order  of  creatures  of  which 
the  different  individuals  bear  so  little  resemblance  to  each 
other.  The  organization  of  the  corallines,  flustras,  sertu- 
larias,  and  other  orders  of  marine  zoophytes  may,  however, 
be  illustrated  by  that  of  the  Hydra,  or  common  fresh-water 
polype.  These  animals,  which  resemble  little  pieces  of  jelly, 
are  found  in  ponds  or  slowly  running  streams,  attached  to 
the  under  surface  of  the  leaves  of  aquatic  plants,  or  to  any 
floating  substance,  such  as  a  stick  or  a  straw.  They  are 
remarkable  for  the  extreme  simplicity  of  their  organiza- 
tion, which  consists  of  nothing  but  a  digestive  cavity  or 
stomach,  surrounded  by  a  fringe  of  long  thread-like  arms 
or  movable  tentacula,  by  means  of  which  the  animal  pro- 
cures its  food — generally  some  minute  insect  or  worm, 
which  it  seizes  with  a  tendril-like  grasp  and  instantly  con- 
veys into  its  stomach  by  a  contractile  effort.  The  contrac- 
tility* of  the  tentacula  of  the  Hydra  is  truly  wonderful, 
When  the  animal  is  hungry  and  in  search  of  prey,  the  ten- 
tacula are  extended  to  a  distance  of  not  less  than  six  or 
seven  feet  from  the  mouth  of  the  stomach ;  but  when  the 
digestive -cavity  is  filled  with  food  and  the  wants  of  the 
animal  are  appeased,  they  are  so  contracted  as  to  appear 
only  like  tubercles  around  its  entrance. 

The  different  species  of  corallines,  flustras,  and  sertu- 
larias,  usually  found  attached  to,  or  more  frequently 
intermingled  with,  the  sea-weed  cast  upon  our  shores,  con- 
sist of  an  association  of  polypes  having  individually  a  simi- 
lar organization  to  the  Hydra,  but  united  together  about 
a  common  axis  of  growth  like  the  buds  and  branches  of 


18  INTRODUCTION. 

a  plant.  It  is  interesting  to  trace  the  analogies  between 
the  members  of  the  animal  and  vegetable  kingdom  in  the 
lower  orders  of  animated  nature.  The  sertularian  polypes 

Fig.  2. 


Fig.  2.    a.  Sertularia  or  compound  polype.    &.  Magnified  view  of  a  portion  of 
its  branches,  showing  the  polype  buds. 

with  their  common  stalk  bearing  numerous  individuals, 
have  in  every  instance  been  produced  by  continuous 
growth  from  a  single  individual.  Here  we  have  a  repe- 
tition of  similar  parts  precisely  as  in  plants.  There  can 
be  no  mistake  as  to  the  vegetative  nature  of  these  actions. 
Each  of  these  associated  polypes  has  an  independent  vi- 
tality of  its  own,  and  yet  all  depend  on  the  general  life 
diffused  through  the  entire  community.  They  individually 
capture  and  digest  their  prey  like  the  Hydra,  and  yet  the 
products  of  their  individual  digestion  are  applied  not  only 
to  their  own  support  but  to  that  of  the  general  axis ;  for 
the  stomachs  of  the  several  polypes,  communicate  with 
each  other  by  means  of  a  tube  which  proceeds  from  the 
base  of  each  into  the  common  digestive  cavity  of  the  stem. 
Some  of  these  polype  buds  periodically  die  and  are  cast 
off  like  the  leaves  of  a  tree  j  whilst  others,  retaining  their 


INTRODUCTION.  19 

vitality,  spontaneously  detach  themselves  and  evolve  into 
similar  fabrics  elsewhere. 

It  is,  however,  amongst  .the  algae  that  vegetable  and 
animal  life  appear  to  be  the  most  completely  blended  to- 
gether. It  is  well  known  to  naturalists  that  the  spores  of 
some  of  our  common  fresh  water  algae,  as  for  instance,  con- 
ferva glomerata  and  prolifera  rivularis,  when  first  dis- 
charged into  the  water,  move  about  by  means  of  certain 
ciliary  appendages  during  a  certain  period  of  their  life.  At 
this  stage  of  development  they  were  observed  by  Ehren- 
berg,  and  were  actually  figured  by  him  as  infusoria.  After 
awhile,  however,  their  cilias  are  absorbed,  their  motions 
cease,  they  become  attached  to  some  substance  in  the 
stream,  and  develop  into  plants  fixed  and  immovable  ex- 
cept from  the  influence  of  the  current.  It  would  appear 
from  this,  that  these  simple  unicellular  organisms  are 
animals  during  the  first  period  of  their  life  and  vegetables 
towards  its  close. 

All  organized  matter,  whether  animal  or  vegetable,  con- 
sists of  cells,  and  life  is  only  known  to  us  as  manifested 
through  their  agency.  Not  only  may  every  animal  and 
plant  be  traced  to  a  simple  cell,  but  organic  nature  is  evi- 
dently only  a  series  of  forms  which  exhibit  the  successive 
stages  of  its  development.  The  animal  and  plant  seem  to  be 
blended  together  in  this  the  primitive  form  of  all  organized 
being.  It  is  here  that  the  last  signs  of  animality  disappear, 
after  which,  life  becomes  wholly  vegetative. 

It  is  not  then  among  vegetables  and  animals  the  most 
highly  organized,  that  we  find  the  most  striking  analogies 
between  the  animal  and  vegetable  kingdoms,  but  it  is  those 
which  possess  the  greatest  amount  of  structural  simplicity, 
that  approximate  the  most  closely  to  an  identity  of  function. 

The  assemblage  of  organized  beings  denominated  animals 


20  INTRODUCTION. 

and  plants,  may  be  collectively  represented,  in  reference  to 
their  mutual  relationship,  by  two  cones,  one  of  which  is  in- 
verted on  the  other,  so  that  their  summits  are  brought  into 
mutual  contact.  For  there  is  a  point  of  departure  common 
to  both  of  these  grand  divisions  of  living  nature, — THE 
ORGANIC  CELL, — which  animated,  commences  the  animal 
series,  and  remaining  immovable,  serves  as  the  basis  of  the 
vegetable  creation.  This  organic  cell  may  be  imagined  to 
be  situated  at  the  apex  of  the  cones,  the  lower  cone  repre- 
senting the  vegetable  and  the  upper  one  the  animal  creation. 
Plants  and  animals  increase  in  organic  simplicity  and  the 
analogies  between  them  multiply  and  become  more  striking 
in  proportion  to  their  approach  to  this  point ;  while,  on  the 
contrary,  the  differences  which  separate  them  increase  and 
their  organization  becomes  more  complicated,  as  they  elon- 
gate from  it. 

All  that  variety  of  form  which  marks  the  external 
organs  both  of  plants  and  animals,  is  clearly  traceable  to 
the  same  organic  laws.  Thus,  the  same  organ  which  attains 
a  high  degree  of  development  in  one  plant  or  animal,  is  for 
certain  physiological  reasons  in  another,  either  suppressed 
altogether  or  reduced  to  a  rudimentary  condition.  But 
these  changes  take  place  almost  imperceptibly.  We  never 
see  an  important  organ  disappear  all  at  once  in  any  of  the 
classes  of  the  animal  and  vegetable  kingdom.  It  is  by  de- 
grees that  the  organ  loses  in  succession  the  several  parts 
which  complicated  it ;  these  become  rudimentary,  and  the 
organ  is  finally  reduced  to  the  utmost  degree  of  structural 
simplicity,  those  parts  alone  remaining  which  are  absolutely 
essential  to  enable  it  to  perform  its  function.  What  are 
called  varieties  by  naturalists  are,  in  fact,  only  different 
phases  in  the  organic  development  of  the  same  specific 
form  j  and  a  truly  scientific  classification  can  only  be 


INTRODUCTION.  21 

achieved  in  proportion  to  the  accuracy  of  our  perceptions  of 
the  natural  relationship  subsisting  among  the  organs  thus 
modified. 

The  anterior  organs  of  the  different  order  of  vertebrated 
animals,  for  instance,  are  organically  modified  to  the  degree 
of  their  intelligence,  their  powers  of  locomotion,  and  their 
peculiar  habits.  In  some  quadrupeds  they  are  adapted  for 
the  prehension  of  food  and  for  locomotion ;  in  the  bird  they 
are  organized  for  flight ;  in  the  fish,  for  balancing  the  body 
and  assisting  its  progress  through  the  water.  The  twisted 
arm  of  the  tortoise  can  be  applied  to  no  other  purpose  than 
that  of  creeping,  and  the  enormous  hand  of  the  mole  can  be 
used  only  for  burrowing.  Yet  the  anterior  members  in  the 
different  orders  of  the  vertebrata  consist  essentially  of  the 
same  parts  as  those  which  exist  in  the  same  members  in 
man.  We  find  in  each  the  same  bones,  muscles,  nerves, 
and  vessels.  Yet  how  different  their  appearance  !  how 
varied  their  functions !  All  these  ends  are  attained  by  a 
modification  in  the  development  of  the  different  parts,  one 
bone  being  largely  developed,  a  contiguous  one  less  so, 
some  being  evolved  to  a  maximum,  whilst  others  are  left 
rudimentary. 

We  have  a  manifestation  of  the  same  organic  law  in  the 
vegetable  world.  Thus  the  leaves  of  plants  are  variously 
modified  so  as  to  be  rendered  subservient  to  the  exercise  of 
the  different  vegetative  functions.  The  different  organs 
appended  to  the  vegetable  axis  and  designated  as  scales, 
stipules,  bracts,  sepals,  petals,  stamens,  and  pistils,  are  only 
a  series  of  leaves  in  a  state  of  progressive  or  retrograde  de- 
velopment, which  have  assumed  this  peculiarity  of  form  in 
consequence  of  the  peculiar  and  distinct  functions  assigned 
them.  A  fully  developed  leaf  consists  of  two  parts,  a  little 
stalk  or  support  called  a  petiole,  and  a  flat  expanded  por- 


22  INTRODUCTION. 

tion  called  the  blade  or  limb.  In  the  scale,  stipule,  and 
bract,  the  petiole  and  lamina  of  the  leaf  are  reduced  to  rudi- 
mentary condition ;  in  the  sepal  the  former  is  wholly  sup- 
pressed and  the  latter  more  or  less  developed.  In  the  petal 
both  lamina  and  petiole  are  sometimes  present,  as  in  the 
pink  and  wall-flower.  The  petals  of  these  flowers  which  are 
broad  and  expanded  at  their  summit  gradually  taper  into  a 
narrow  stalk  or  petiole,  which  in  this  instance  is  called  an 
unguis,  or  claw.  In  the  stamen,  the  petiole  is  represented 
by  the  filament,  the  lamina  by  the  anther,  whilst  the  repro- 
ductive matter  called  pollen,  which  is  contained  in  the 
anther-cells,  is  only  a  peculiar  transformation  of  the  paren- 
chyma of  the  leaf.  In  the  pistil,  there  appears  to  be  the 
greatest  departure  from  the  primitive  type ;  yet  it  is  not 
difficult  to  trace  it  even  in  this  instance.  The  pistil  is 
nothing  but  a  folded  leaf,  the  margins  of  which  have  united 
to  form  a  placenta  or  point  of  attachment  for  the  ovules, 
or  young  germs,  which  develop  along  its  edge.  Other  in- 
stances might  be  brought  forward  illustrative  of  the  fact 
that  the  same  laws  of  development  and  adaptation,  govern 
the  organization  of  both  plants  and  animals. 

It  is  only  by  viewing  nature  as  a  whole  that  any  part  of 
nature  can  be  properly  understood.  It  is  to  the  study  of 
comparative  anatomy  and  physiology,  that  we  are  indebted 
for  our  knowledge  of  this  identity  and  unity  of  organization. 
The  organism  of  one  species  has  been  compared  with  that 
of  another,  and  the  transitions  forms  of  the  several  organs 
have  been  traced,  so  that  organs  are  now  recognized  as  the 
same  which  were  formerly  thought  to  be  altogether  different. 
It  is  to  the  contributions  which  they  mutually  afford  each 
other  that  we  are  indebted  for  the  advance  of  the  physical 
sciences,  and  the  same  principle  applies  to  natural  history. 
Almost  every  part  of  the  human  frame  has  its  homologue 


INTRODUCTION.  23 

in  some  inferior  animal.  Hence  "the  advantage — the 
necessity,  rather — of  combining  a  general  knowledge  of  the 
organization  of  the  lower  animals  with  that  of  man,  which 
ought  always  to  claim  the  first  attention  of  the  medical 
student,  is  now  universally  recognized.  A  great  part,  of 
the  best  part,  of  the  proofs  of  the  most  important  physio- 
logical doctrines  are  derived  from  comparative  anatomy. 
The  increasing  taste  for  the  natural  sciences,  and  the  rapidly 
diffusing  knowledge  of  zoology  and  geology  render  it  scarcely 
pardonable  in  a  member  of  a  liberal  profession  to  be  wholly 
unversed  in  them,  and  almost  discreditable  to  a  medical 
man  to  be  unable  to  offer  any  sound  opinion  on  a  fossil 
coral,  shell,  or  bone,  which  may  be  submitted  to  his  inspec- 
tion."* So  also,  the  great  cell  doctrine  which  is  now  the 
basis  of  animal  physiology,  had  its  origin  in  microscopical 
investigations  into  the  organization  of  plants.  "  Since  it 
has  been  ascertained  that  the  animal  tissues  are  in  their 
fundamental  structure  identical  with  the  vegetable  tissues, 
we  may  expect  that  botanical  investigations  may  throw  as 
much  light  upon  the  animal  kingdom,  as  the  study  of  ani- 
mals may  throw  on  the  vegetable  kingdom.  Easy  as  it  has 
been  to  study  the  structure  of  vegetable  tissues,  so  difficult 
has  it  been  to  ascertain  their  functions,  and  the  work  of  the 
various  organs  in  plants,  that  the  most  contradictory  opi- 
nions are  entertained  upon  vegetable  functions,  upon  the 
circulation  of  their  sap,  upon  their  respiration,  and  the 
action  of  respiration  on  their  fluids.  On  the  contrary,  in 
animal  structures  the  functions  are  easily  traced.  The  com- 
bined action  of  the  various  functions  upon  each  other  can 
be  easily  ascertained.  It  was  the  structure,  the  intimate 

*  Lectures  on  the  Comparative  Anatomy  and  Physiology  of  the 
Invertebrate  Animals,  delivered  at  the  Royal  College  of  Surgeons :  by 
Richard  Owen,  F.  R.  S. 


24  INTRODUCTION. 

structure  which  it  was  difficult  to  investigate.  And  now 
by  referring  the  result  from  one  kingdom  to  the  other,  it  is 
to  be  hoped  that  much  more  rapid  progress  will  be  obtained 
than  before."*  Many  problems  connected  with  nutrition 
and  reproduction  in  animals  will  probably  be  solved  by  a 
more  careful  observation  of  these  functions  in  vegetables. 
A  knowledge  of  cell-life,  now  universally  admitted  to  be 
the  basis  of  all  scientific  physiology,  can  be  best  acquired 
by  examining  the  cells  of  plants  which  are  much  larger 
than  those  of  animals,  and  visible  to  ordinary  microscopes 
at  every  epoch  of  their  development.  The  differences  which 
exist  among  the  organic  productions  are  not  so  great  as  is 
commonly  thought.  There  is  a  oneness  in  nature  which 
has  yet  to  be  understood  and  appreciated. 

One  of  the  most  striking  differences  of  organization  be- 
tween the  higher  orders  of  animals  and  plants  consists  in 
the  presence  of  a  nervo-muscular  system  in  the  former  of 
which  the  latter  are  totally  deprived.  This  nervo-muscular 
system,  which  is  essential  to  animality,  appears  to  be  gradu- 
ally developed  in  vegetable  life,  which  thus  becomes  in- 
separably bound  up  with  the  exercise  of  the  animal  func- 
tions. It  is  gradually  developed  in  the  inferior  orders  of 
animated  being,  and  is  manifested  most  perfectly  in  man, 
and  those  animals  the  most  closely  allied  to  him  in  organi- 
zation. 

Now  comparative  anatomy  shows  that  the  animal  func- 
tions of  sensation  and  voluntary  motion,  manifest  themselves 
in  proportion  to  the  more  or  less  perfect  condition  of  the 
organs  appropriated  to  their  exercise.  In  man,  the  highest 
vertebral  animal,  the  organs  of  the  senses  and  the  muscular 

*  Lectures  on  Comparative  Embryology,  delivered  before  the  Lowell 
Institute  in  Boston,  by  Louis  Agassiz. 


INTRODUCTION.  25 

system  are  the  most  highly  developed,  and  prove  successive 
degrees  of  simplification  as  we  descend  in  the  scale.  The 
muscles  in  the  human  body  are  more  than  five  hundred  in 
number,  and  almost  every  movement  is  produced,  not  by 
the  action  of  one,  but  of  several  of  them.  The  muscular 
system  in  man  not  only  moves  the  body  but  expresses 
thought  and  emotion,  and  is  capable  of  a  very  high  degree 
of  education.  The  accomplished  tragedian  and  musician 
manifest  in  their  performances,  the  degree  to  which  the 
muscles  of  expression  and  voluntary  motion  may  be  educated. 
The  body  of  man  is  capable,  through  the  agency  of  his  highly 
developed  nervo-muscular  system,  of  an  infinite  variety  of 
movement  and  expression.  In  man,  the  muscles  of  expres- 
sion are  chiefly  in  the  face.  In  conversation,  all  persons  to 
a  greater  or  less  extent  communicate  thought  by  the  expres- 
sion of  their  countenance.  In  some,  however,  the  muscles 
of  expression  respond  more  readily  to  the  emotions  of  the 
mind  than  in  others,  every  shade  of  thought  and  feeling 
being  beautifully  depicted  in  their  faces.*  In  the  inferior 
animals,  the  expression  of  which  they  are  capable  is  much 
more  limited,  and  is  confined  to  other  parts  of  the  body. 
The  dog  wags  his  tail,  the  cat  elevates  her  back,  the  horse 
erects  his  ears,  and  the  game-cock  spreads  out  his  ruff  of 
feathers  on  his  head.  The  countenance  of  the  inferior  ani- 
mals is  in  general  devoid  of  expression.  Kage  and  fear  are 
almost  the  only  passions  which  are  expressed  in  their  faces. 
Their  muscular  movements  are  susceptible  of  education,  as 
is  evident  from  the  performances  of  dancing  dogs  and  bears, 


#  Human  Physiology  designed  for  Colleges  and  the  Higher  Classes 
in  Schools,  and  for  General  Reading,  by  Worthington  Hooker,  M.  D., 
Professor  of  the  Theory  and  Practice  of  Medicine  in  Yale  College. 
Chapter  xiii.  page  222. 

3 


26  INTRODUCTION. 

but  not  to  the  same  extent  as  those  of  man,  owing  to  the 
low  degree  of  their  intelligence. 

The  organs  of  the  anterior  and  posterior  extremities 
connected  with  the  trunk  or  spinal  column  in  the  higher 
vertebrata,  are  gradually  absorbed  in  the  lower,  until  at 
length  in  the  serpent  tribe,  these  locomotive  appendages  are 
suppressed  altogether,  and  the  body  of  the  animal  consists 
of  little  else  but  the  spinal  column  itself,  which  is  very 
long  and  extremely  flexible,  owing  to  the  immense  num- 
ber of  vertebra,  and  their  connection  with  each  other  by  a 
ball  and.  socket  joint.  The  perceptions  of  the  animal  are 
now  obtuse,  and  all  its  movements  sluggish, — a  mere 
trailing  of  the  body  along  the  ground. 

The  same  gradual  simplification  of  the  nervo-muscular  ap- 
paratus, may  be  traced  throughout  the  descending  series  of 
invertebrated  animals.  Insects  may  be  truly  regarded  as  the 
most  highly  developed  of  the  invertebrata.  In  them  the  ani- 
mal functions  are  decidedly  more  developed  than  the  vegeta- 
tive. Their  rapidity  of  motion,  and  extraordinary  display  of 
intelligence,  entitle  them  to  this  position.  The  tegumentary 
skeleton  of  insects  is  composed  of  a  number  of  movable 
pieces  articulated  to  each  other,  and  is  of  a  horny  texture. 
This  integument  becomes  progressively  hardened,  and  the 
pieces  fewer  in  number,  and  more  consolidated  in  the 
different  orders  of  the  Crustacea,  so  that  the  movements  are 
necessarily  much  more  restricted  and  confined.  In  the 
testaceous  mollusca,  the  integument  is  finally  reduced  to  a 
pair  of  valves,  and  the  muscular  movements  of  the  animal 
are  of  the  simplest  character.  Most  of  the  bivalve  muscles, 
such  as  the  cardium,  move  along  by  means  of  a  fleshy  organ 
called  a  foot.  The  movements  of  the  oyster  are  restricted 
to  the  single  act  of  opening  and  closing  its  shell,  and  those 
of  serpulae  and  limpets,  to  the  alternate  protrusion  and 


INTRODUCTION.  27 

withdrawal  of  their  tentacula  within  their  testaceous  cove- 
ring. What  a  contrast  do  the  simple  motions  of  these 
animals  present  to  the  complicated  motor  machinery  of  the 
human  frame !  How  immense  the  chasm  of  separation 
between  these  creatures  and  man  ! 

The  laws  of  phenomena  really  constitute  science,  and 
facts  ought  ever  to  be  made  subservient  to  their  discovery. 
The  zoologists  and  botanists  who  devote  all  their  time  and 
attention  to  the  mere  business  of  collecting  species,  of  de- 
fining their  external  characters,  and  of  forming  systematic 
arrangements  of  them,  undoubtedly  perform  a  great  and 
valuable  service ;  but  this  after  all,  is  but  a  coarse  outline 
of  the  natural  history  of  any  country.  It  is  not  sufficient 
to  obtain  specimens  of  natural  history  for  the  cabinet,  to 
group  plants  and  animals  according  to  their  outward 
appearance ;  we  must  look  more  deeply  into  the  mysteries 
of  their  organization,  we  must  study  their  physiology  and 
the  laws  of  their  development.  It  is  true  that  little  pro- 
gress can  be  made  in  these  investigations  without  we  avail 
ourselves  of  the  labors  of  the  systematist ;  but  after  all,  the 
technical  description  of  the  external  organs  of  plants  and 
animals,  is  only  the  infancy  of  science.  It  is  not  sufficient 
that  we  make  ourselves  acquainted  with  facts  we  must 
study  their  philosophy. 

For  example,  it  is  well  known  to  botanists  that  the  calyx 
of  the  bloodroot  (Sanguinaria  Canadensis,)  drops  from  the 
flower  stem  as  soon  as  the  petals  open  and  expand,  whilst  in 
the  blackberry  (Rubus  villosus;,)  it  survives  the  decay  and 
removal  of  the  other  parts.  Why  do  the  cells  of  the  calyx 
perish  at  so  early  period  in  the  one  instance,  and  remain 
persistent  about  the  fruit  in  the  other  ?  What  is  it  that  pro- 
duces their  early  decay  or  the  prolongation  of  their  vitality  ? 
This  is  a  very  simple  question,  and  yet  in  the  present  state 


28  INTRODUCTION. 

of  science,  it  is  impossible  to  give  the  reader  a  satisfactory 
answer.  All  botanists  are  acquainted  with  the  fact,  its 
philosophy  is  unknown.  Every  branch  of  natural  history 
is  more  or  less  in  this  imperfect  condition.  Botany  is 
perhaps  the  most  defective.  It  is  in  truth  very  little  better 
than  an  accumulation  of  sterile  facts.  He  who  studies 
botany  or  any  other  branch  of  natural  history  in  this,  the 
true  philosophical  spirit,  will  not  fail  of  becoming  an  origi- 
nal contributor  to  the  department  which  he  undertakes. 
In  the  place  of  a  narrow  circumscribed  science,  he  will  find 
an  immense  field,  in  which  the  commonest  and  most  insig- 
nificant weed  or  animal,  will  furnish  him  with  innumerable 
subjects  for  reflection  and  study. 


PART  I. 


HISTOLOGY  OF  PLANTS  AND  ANIMALS. 


CHAPTER  I. 

ON   THE   INDIVIDUALITY   OF   THE   CELLS. 

EVERY  plant,  germinating  from  the  seed  or  spore,  is  sub- 
ject from  the  commencement  of  germination  to  the  close  of 
its  allotted  period  of  life,  to  certain  definite  laws  of  develop- 
ment which  are  impressed  on  the  cells  of  which  that  seed 
or  spore  consists. 

If  we  consider  the  cells  collectively  as  associated  together 
in  masses,  constituting  definite  organs,  the  regularity  and 
fixity  of  form  assumed  by  those  organs,  shows  that  a  certain 
definite  number  of  cells  must  be  developed  to  form  them, 
and  that  these  cells  must  attain  a  determinate  amount  of 
expansion;  for  growth,  or  the  enlargement  of  the  organs  of 
plants,  certainly  appears  to  be  as  much  the  result  of  the 
expansion  of  cells  already  existing,  as  of  the  formation  of 
new  cells. 

But  the  cells  themselves,  regarded  individually,  exhibit 
a  series  of  phenomena  which  prove  that  they  are  subject  to 
laws  of  development  as  rigid  and  invariable  as  those  which 
govern  them  collectively.  The  primitive  form  of  all  cells, 
whether  animal  or  vegetable,  is  that  of  a  closed  spherical 
vesicle  or  utricle.  There  is  no  plant,  or  organ  of  a  plant, 
which  is  not  at  the  commencement  of  its  growth,  fabricated 
exclusively  of  cells  which  approach  more  or  less  to  that  of 
a  sphere  in  form.  If  we  examine  a  bud,  a  young  leaf  or 
rootlet,  with  the  microscope,  in  the  first  stages  of  growth, 
we  shall  find  that  cells  which  retain  in  a  great  measure 
their  primitive  sphericity,  and  present  the  same  uniform 


32  THE  TISSUES  OF  PLANTS 

appearance  in  their  external  configuration,  constitute  the 
substance  of  each  of  these  organs.  At  this  stage  of  growth 
the  cells  are  all  apparently  the  same,  and  endowed  with 
similar  functions;  but  that  this  is  not  really  the  case,  is 
shown  by  their  subsequent  behavior  in  their  after  develop- 
ment. It  is  only  in  plants  which  are  very  low  in  organi- 
zation, such  as  algae  and  lichens,  that  the  cells  permanently 
retain  this  primitive  and  uniform  appearance;  in  vegetation 
of  a  higher  grade,  this  uniformity  speedily  disappears,  and 
the  individuality  of  the  cells  becomes  manifest  as  growth 
progresses.  Whilst  some  of  them  continue  spherical, 
others  take  a  much  higher  degree  of  development,  and  be- 
come gradually  transformed  into  woody  fibre,  vascular 
tissue,  and  spiral  vessels. 

We  say  that  certain  determinate  cells  only,  thus  change 
their  character.  This  is  apparent  on  the  cross  section  of 
the  stem  of  any  herbaceous  exogen,  which  has  just  begun 
to  grow,  and  to  unfold  its  first  sets  of  leaves.  It  will  be 
seen  that  the  cells  in  the  centre  and  towards  the  circum- 
ference of  the  stem,  which  form  collectively  the  pith  and 
the  bark,  together  with  those  of  the  medullary  rays,  are 
only  slightly  altered  by  mutual  pressure  from  the  spherical 
form.  Those,  on  the  contrary,  which  constitute  the  wood, 
and  which  occupy  an  intermediate  position  between  the 
bark  and  the  pith,  are  so  changed  in  appearance  that  it 
seems  at  first  impossible  to  refer  them  to  the  same  common 
type.  If  we  examine  a  longitudinal  section  of  the  stem, 
the  nature  and  extent  of  the  transformation  which  the  wood 
cells  have  undergone,  will  be  rendered  more  apparent.  It 
will  be  seen  that  the  fibrous  portion  of  the  wood  consists  of 
elongated,  and  extremely  attenuated  cells,  which  taper  to 
either  extremity  and  lie  together  in  bundles,  and  that 
there  are  intermingled  with  these  fibres  several  varieties  of 


COMPARED  WITH  THOSE  OF  ANIMALS. 


33 


vasiform  tissue  and  spiral  vessels,  the  last  being  particularly 
abundant  in  the  neighborhood  of  the  pith. 

Fig.  3. 


Longitudinal  section  of  Italian  reed,  a,  Cells  of  the  pith ;  b,  annular  ducts ; 
e,  spiral  duct ;  d,  dotted  duct ;  e,  woody  fibre ;  /,  cells  of  the  herbaceous  integu- 
ment, one  of  the  epidermal  layers. 

It  is  not  difficult  to  follow  this  transformation  through  its 
successive  stages,  and  thus  to  arrive  satisfactorily  at  the  im- 
portant physiological  fact  of  the  individuality  of  the  cells. 
It  is  only  necessary  first  to  examine  the  stem  or  any  other 
organ  in  the  embryonic  condition,  and  then  at  intervals, 
soon  after  active  life  has  begun  to  manifest  itself  in  the 
germ. 

If  we  observe  the  fibrous  portion  of  the  wood,  for  instance, 
when  germination  commences,  we  shall  see  that  at  first  the 
fibre  cells  consist  of  a  row  of  utricles  somewhat  more 
elongated  than  the  neighboring  cells ;  gradually  these 


34  THE  TISSUES  OF  PLANTS 

elongated  utricles  become  lengthened  into  tubes,  and  the 
septa  or  partitions  which  separate  them,  and  which  in  this 
instance  are  not  absorbed,  assume  an  oblique  position  with 
reference  to  their  interior. 

The  different  varieties  of  vasiform  tissue  or  ducts  will 
be  seen  to  originate  like  the  woody  fibre  from  a  row  of 
elongated  utricles;  but  the  membrane  which  forms  the 
walls  of  the  fibre  cells  appears  to  be  more  susceptible  of  ex- 
tension than  that  of  the  duct  cells.  Both  the  transverse 
and  lateral  walls  of  the  row  of  utricles  which  form  the  fibre 
cells  are  elongated,  and  this  takes  place  owing  to  the  great 
tenacity  and  extensibility  of  ..the  walls  of  the  several 
cellules,  without  any  rupture  or  open  communication  be- 
tween them  being  effected.  Hence  it  is  that  the  fibre  cells 
overlap  each  other  at  their  extremities,  or  are  as  it  were 
spliced  together,  and  their  calibre  or  bore  must  necessarily 
diminish  in  proportion  to  the  degree  of  their  attenuation. 
It  is  in  fact  reduced  to  the  very  finest  degree  of  capillarity, 
so  that  the  tubular  character  of  the  fibre  cells  can  only  be 
verified  by  employing  the  very  highest  powers  of  the  best 
microscopes.  The  parietes  of  the  row  of  utricles  which 
originate  the  several  varieties  of  vasiform  tissue  or  duct 
cells,  on  the  other  hand,  will  not  submit  to  a  similar  degree 
of  tension ;  on  the  contrary,  a  very  slight  degree  of  elonga- 
tion is  sufficient  to  rupture  the  cross  walls  of  the  several 
cells,  so  as  to  form  a  continuous  communication  between 
them.  An  uninterrupted  tube  with  a  conspicuous  calibre 
or  bore,  is  the  natural  result.  These  ducts  are  generally 
situated  on  the  inner  side  of  the  circle  of  fibre  cells,  and 
their  open  mouths  are  not  unfrcquently  visible  on  the  cross 
section  without  the  aid  of  the  microscope  in  the  form  of 
rounded  openings  or  pores. 

In  their  earliest  condition,  the  cells  of  animals,  like  those 


COMPARED  WITH  THOSE  OF  ANIMALS.  35 

of  plants,  present  the  same  uniformity  of  appearance  in 
their  external  configuration.  Some  of  them  maintain  this 
condition  throughout  the  life  of  the  animal,  and  are  the  in- 
struments by  which  the  strictly  vital  operations  are  carried 
on ;  others  rapidly  undergo  a  change  of  form  in  accordance 
with  those  laws  of  growth  to  which  they  are  individually 
subject.  In  this  respect  precisely,  the  same  laws  govern 
both  the  animal  and  vegetable  world.  "  A  globular  mass," 
says  Carpenter,  "  containing  a  large  number  of  cells  is 
formed  before  any  diversity  of  parts  shows  itself ;  and  it  is 
by  the  subsequent  development  from  this  mass  of  different 
sets  of  cells,  of  which  some  are  changed  into  cartilage,  others 
into  nerve,  others  into  muscle,  others  into  vessels,  and 
so  on,  that  the  several  parts  of  the  body  are  ultimately 
formed." 

There  is,  however,  one  distinction  between  the  cells  of 
plants  and  animals  which  must  not  be  overlooked.  It  con- 
sists in  the  fact  that  the  cells  of  plants  are  rnu^h  larger  than 
those  of  animals,  and  retain  all  the  characteristics  of  cells 
throughout  the  life  of  the  plant,  so  that  a  cross  section  of 
any  part  of  the  vegetable  fabric  will  at  any  time  show  them. 
But  the  cells  of  animals  rapidly  undergo  a  development  into 
tissues  in  which  the  cellular  form  wholly  disappears.  Hence 
it  is  that  the  cellular  origin  of  many  of  the  .animal  tissues 
can  only  be  detected  in  the  ovum ;  in  the  fully  developed 
embryo  all  appearance  of  cell  and  nucleus  has  vanished. 
Thus  whilst  the  cellular  origin  and  structure  of  plants  has 
been  long  known,  that  of  animals  is  to  be  enumerated 
amongst  the  discoveries  of  modern  times. 

As  an  instance  of  this  gradual  obliteration  of  the  nucleus 
and  cell  wall,  we  refer  to  those  cells  which  originate  the 
more  permanent  and  solid  parts  of  the  animal  body ;  such, 
for  example,  as  the  teeth  of  man,  or  the  shells  of  the  mol- 


36 


THE  TISSUES  OF  PLANTS 


lusca.  At  first  these  parts  consist  of  cells  more  or  less 
closely  connected  together,  either  by  a  general  enveloping 
membrane,  or  by  an  intercellular  substance  which  holds 
them  together  by  its  adhesive  properties. 

Fig.  4. 


Fig.  4  represents  a  portion  of  one  of  the  animal  layers 
included  between  the  calcareous  laminse  of  a  bivalve  shell ; 
in  which  are  <shown  at  «,  nuclei  forming  in  the  midst  of  a 
plastic  fluid  prepared  and  elaborated  by  the  cells  of  a  pre- 
vious generation;  b,  the  same  advanced  to  the  condition  of 
incipient  cells;  c,  the  cells  more  developed  but  still  sur- 
rounded by  the  fluid ;  d,  the  cells  in  close  contact  with 
each  other,  and  rendered  polygonal  by  mutual  pressure. 

These  last  cells  in  the  enamel  of  the  teeth  attract  phos- 
phate of  lime  into  their  cavities,  whilst  those  which  form 
the  shelly  covering  of  the  mollusca  become  filled  with  cal- 
careous matter.  The  walls  of  the  cells  now  disappear  and 
there  is  a  coalescence  of  their  cavities,  so  that  the  solid  mass 
appears  altogether  homogeneous,  retaining  not  a  single 
trace  of  its  cellular  origin. 

In  some  cases,  however,  the  cellular  character  of  the 
tissue  is  maintained  throughout  the  life  of  the  animal. 
Thus,  what  is  commonly  called  fat,  consists  of  a  mass  of 


COMPARED  WITH  THOSE  Or  ANIMALS.       37 

globular  or  dodecahedral  cells  containing  fat  in  their  interior, 
to  which  the  term  adipose  tissue  is  applied,  in  works  on  ana- 
tomy and  physiology. 

Fig,  5. 


Cells  of  adipose  tissue. 

These  cells  may  be  seen  *at  any  time,  even  with  micro- 
scopes of  a  very  inferior  quality.  They  retain  their  original 
cellular  form,  and  hence  the  cellular  character  of  adipose 
tissue  has  been  long  known. 

The  number  of  tissues  in  the  animal  is  much  greater 
than  in  the  plant.  Their  morphology  from  the  same  cellu- 
lar type  is  still  a  matter  which  requires  further  elucidation. 
Their  differences,  like  those  of  plants,  are  not  always  well- 
marked,  one  form  of  animal  tissue  passing  into  another  by 
insensible  shades  of  gradation.  In  man  and  other  animals 
of  a  high  grade  of  organization,  the  tissues  are  by  far  the 
most  numerous  and  well-defined.  As  we  descend  in  the 
chain  of  being,  these  distinctions  between  the  tissues  become 
gradually  effaced,  the  organs  are  not  so  numerous,  and  the 
whole  structure  is  greatly  simplified.  The  soft  body  of  a 
snail,  for  example,  is  much  more  uniform  in  its  composi- 
tion than  the  body  of  a  bird  or  a  quadruped.  The  parts 
of  the  osseous  frame-work  are  gradually  blended  together, 
the  bones  become  cartilaginous,  and  finally  disappear 
4 


38  THE  TISSUES  OF  PLANTS 

altogether  from  the  organism,  as  in  the  medusae  or  jelly 
fishes.  At  length  we  arrive  at  animals  whose  bodies  are 
made  up  of  nothing  but  cells  in  contact  with  each  other, 
and  which  permanently  retain  that  uniformity  of  appearance 
presented  by  every  kind  of  tissue,  whether  animal  or  vege- 
table, in  the  first  stages  of  its  development.  Such  is  the 
case  with  the  vast  tribe  of  the  infusorial  animals,  so  called 
because  they  abound  in  decaying  animal  and  vegetable  in- 
fusions. These  animals  move  about  in  the  water  by  means 
of  little  hair-like  organs  at  their  surface,  which  are  them- 
selves merely  modified  cells.  These  creatures  have  been  very 
appropriately  named  protozoa,  as  they  hold  a  corresponding 
rank  in  the  animal  creation  to  the  protophytes  in  the  vege- 
table. Thus  animals  and  plants  are  alike  in  their  gradually 
increasing  simplicity  of  organization,  as  we  approach  the 
cell, — their  primitive  form  and  common  starting  point. 

The  primitive  rounded  form  of  the  cells  is  retained  when- 
ever they  are  loosely  aggregated,  as  in  the  pith  of  most 
herbaceous  plants  and  the  pulpy  part  of  fruits ;  in  the  more 
compact  tissues  of  the  epidermis  and  the  parenchyma  of  the 
leaves  they  are  angular  and  polyhedral.  In  the  greatest 
number  of  cases  each  utricle  is  compressed  into  the  form  of 
a  dodecahedron,  and  therefore  necessarily  exhibits  a  little 
hexagonal  cavity  when  seen  in  section.  Occasionally  these 
dodecahedral  cells  develope  with  the  greatest  geometrical 
regularity;  most  frequently,  however,  they  are  extremely  irre- 
gular in  outline,  some  of  their  walls  growing  at  the  expense 
of  the  others,  which  thus  become  greatly  reduced  in  size  or 
even  suppressed  altogether,  so  that  the  cells  exhibit  on  the 
cross  section  pentagonal,  or  even  cubical,  as  well  as  hexa- 
gonal cavities.  This  is  well  exemplified  in  the  epidermis  of 
Tradescantia  discolor,  the  polyhedral  cells  of  which  are  ex- 
tremely irregular  in  outline.  It  is  not  difficult  to  see  that 


COMPARED  WITH  THOSE  OF  ANIMALS. 


89 


in  this  case  the  hexagonal  is  the  predominating  form, 
although  the  heptagonal,  pentagonal,  and  cubical  varieties 
are  also  represented. 

Fig.  6. 


Irregular  polyhedral  cells  from  the  pith  of  the  elder. 

So^also  cubical" cells  may  become  rectangular  four-sided 
prisms,  or  even  be  so  much  compressed  as  to  assume  the 
appearance  of  fibres,  as  is  fully  seen  in  the  annexed  section 
of  the  rind  of  the  common  gourd. 

Fig.  7. 


Vertical  section  of  the  rind  of  the  gourd. 

Thus,  it  is  evident,  that  cells  may,  to  a  certain  extent, 
change  their  form,  without  changing  their  nature  or  the 
identity  of  their  function. 

When  the  cells  of  plants  are  bounded  by  curved  instead 


40  THE  TISSUES  OP  PLANTS 

of  plane  surfaces,  as  for  instance,  when  they  assume  a 
cylindrical  or  retain  their  spherical  form,  it  is  evident  that 
the  walls  of  contiguous  cells  will  only  come  into  contact  at 
certain  points  of  their  surface,  and  that  triangular  spaces 
will  be  left  between  the  cells.  These  intercellular  passages 
are  beautifully  apparent  between  the  cylindrical  cells  which 
constitute  the  pith  of  the  stem  of  Anemone  Pennsylvania, 
and  afford  the  most  satisfactory  proof  that  these  cells  do  not 
form  a  continuous  and  homogeneous  mass,  but  are  in  reality 
separate  cavities  aggregated  together  and  communicating 
with  each  other  through  their  contiguous  walls. 

Fig.  8. 


riangular  intercellular  canals  between  the  cylindrical  cells  of  Anemone 
Pennsylvanica. 


In  some  instances,  however,  cells  which  are  hexagonal  in 
outline  form  intercellular  passages,  and  this  in  a  manner 
so  interesting  that  it  demands  a  particular  description.  If 
a  section  of  the  young  petiole  of  Sparganium  ramosum  be 
placed  beneath  the  microscope,  a  number  of  triangular 
apertures,  known  to  botanists  as  lacunae,  will  be  seen ;  these 
are  evidently  the  result  of  certain  notches  in  the  cell  walls, 
which  correspond  with  those  in  the  walls  of  contiguous 
cells.  As  growth  progresses  these  notches  become  deeper. 
The  lacunae,  a,  a,  a,  (Fig.  9,)  enlarge  at  the  expense 
of  the  area  enclosed  by  the  cells,  until  at  length  the  cells 


COMPARED  WITH  THOSE  OF  ANIMALS.  41 

assume  a  somewhat  stellated  aspect.  In  Juncus  effusus 
the  common  rush,  we  have  a  beautiful  example  of  this 
kind  of  tissue,  the  cell  being  reduced  to  a  six-rayed  star, 

Fig.  9. 
kASSs 


•s 


Stellate  cells  from  the  petiole  of  Sparganium  ramosum  ;  a,  a,  a,  lacunas. 

as  shown  in  Fig.  10.  In  this  manner  the  large  lacunae 
or  air-cells,  common  in  most  aquatic  plants  are  formed. 

These  air-cells,  or  lacunae,  are  designed  not  only  to  give 
buoyancy  to  the  leaves  and  stems  of  aquatic  plants,  but  also 
to  prevent  their  tissues  from  saturation.  The  air  displaces 
the  water,  which  is  thus  excluded  from  entering  the  tissues 
of  the  plant,  otherwise  than  by  the  ordinary  forces  of  en- 
dosmosis  and  capillarity.  The  formation  of  the  lacunae  is 
not  in  this  instance  the  result  of  a  mere  mechanical  rupture 
of  the  tissues  in  the  interior  of  the  plant,  on  the  contrary, 
they  are  produced  by  a  regular  law  of  development,  im- 
pressed on  certain  cells  of  the  tissue,  which  are  thus 
individualized  and  set  apart  for  this  purpose. 

The  stellate  vegetable  cell  is  of  great  importance  as 
illustrating  the  formation  of  some  of  the  animal  tissues. 
It  is  obvious,  that  if  the  radiating  prolongations  of  the 
cells,  fig.  10,  were  to  coalesce  at  the  points  where  they 
come  into  contact,  so  as  to  throw  together  the  cavities  of 

4* 


42  THE  TISSUES  OF  PLANTS 

the  entire  series,  a  network  of  anastomosing  vessels  would 
be  the  result.  The  capillary  blood-vessels  of  animals  seem 
to  be  produced  in  this  way,  by  the  absorption  of  the  con- 
tiguous parietes  of  their  several  prolongations  at  the  points 
of  junction,  their  cellular  origin  and  original  separation 
being  indicated  by  the  persistent  nuclei  visible  within  their 
-cavities. 

Fig.  10. 


Stellate  cells  from  tlie  stem  of  Juncus  effusus,  the  common  rush. 

But  in  nothing  is  the  individuality  and  independency 
of  the  cells  so  apparent,  as  in  the  varied  character  of  their 
contents.  Generally  speaking,  all  the  cells  of  the  same  tis- 
sue exercise  the  same  function,  and  this  remark  applies 
especially  to  those  which  convey  fluids  and  air,  as  for 
instance  to  the  fibrous  tissue  of  the  wood,  and  the  different 
varieties  of  vasiform  tissue  or  ducts.  The  fibro-vascular 
system  of  plants  is,  in  fact,  altogether  subordinate  in  the 
exercise  of  its  functions  to  those  cells  which  retain  in  a 
great  measure  or  depart  but  slightly  from  their  primitive 
form,  and  which  are  included  under  the  general  term 
parenchyma.  It  is  in  these  cells  that  all  the  organic 
changes  take  place.  The  fibro-vascular  tissue  only  sub- 
serves the  simple  physical  purpose  of  transmitting  the 


COMPARED  WITH  THOSE  OF  ANIMALS.  43 

nutrient  fluid  or  organizable  matter  to  the  cells  of  the 
parenchyma,  which  are  the  true   vegetable  laboratories. 
Endosmosis  and  capillarity  will  account  for  the  ascent  of ' 
the  fluid  in  plants,  and  its  distribution  to  the  remotest  parts 
of  the  organism ;  but  when  the  fluid  enters  the  cell-labo- 
ratories of  the  parenchyma,  its  constituents  are  transmuted 
into  an  immense  variety  of  products  by  processes  which 
have  hitherto   totally  eluded  the   researches   of  science. 
Some  of  these  products,  such  as  chlorophyl,  starch,  gum, 
sugar,  and  raphides,  are  elaborated  more  or  less  by  the 
cells  of  all  plants ;  others  are  restricted  to  certain  species, 
as  for  instance,  the  different  varieties  of  endochrome,  or- 
ganic acids,  resins,  gums,  alkaloids,  fixed  and  volatile  oils. 
In  many  instances  there  is  no  apparent  difference  in  the 
form  of  the  cells,  which  are  closely  united,  forming  part  of 
the  same  parenchyma ;  and  yet  the  diversity  of  their  pro- 
ducts proves  that  they  are  not  the  same  cells.     Thus  we 
have  cells  which  secrete  oils,  resins,  and  different  varieties 
of  endochrome  in  the  midst  of  chlorophyl-secreting  cells ; 
in  proof  of  which  we  refer  the  reader  to  the  oil-cells  which 
produce   the  punctated  appearance  in  the  leaves  of  the 
orange,   to   the   resinous   dotted   foliage   of    Eupatorium 
rotundifolium,  and  to  the  dark  purple  spots  on  the  leaves 
of  Euphorbia  maculata.     Now  since  it  is  a  well  known 
maxim  in  physiology  that  nothing  constant  is  unimportant, 
because  experience  and  observation  both  prove  that  every- 
thing constant  is  connected  with  the  discharge  of  some  es- 
sential function  of  the  organism,  and  as  these  plants  never 
grow  without  a  manifestation  of  these  peculiarities ;  there 
can  be  no  doubt  whatever  that  these  cells  which  produce 
them  have  a  special  and  distinct  work  assigned,  that  they 
are  organically  different  from  those  cells  which  secrete  the 
chlorophyl,  and  that  they  are  separate  co-laborers  in  the 


44  THE  TISSUES  OF  PLANTS 

cell-community,  whose  operations  are  perhaps  as  necessary 
to  the  healthy  discharge  of  the  vital  functions  of  the  plant 
as  that  of  any  other  organ. 

If  we  consider  the  contents  of  the  cells  in  animals,  we 
shall  find  that  they  vary  in  their  character,  and  that  this 
variation  not  unfrequently  gives  an  apparent  color  to  the 
tissues.  We  have  seen  that  in  plants  the  various  and 
beautiful  hues  of  flowers  is  produced  by  fluid  coloring  mat- 
ters which  are  visible  through  the  colorless  walls  of  the 
cells ;  but  in  animal  tissues,  the  coloring  matter  which  is 
called  pigment,  occurs  in  the  cells  m  the  form  of  granules. 
The  most  striking  examples  of  pigment  cells  occur  in  the 
iris  of  the  eye,  in  the  freckles  of  the  skin,  which  are  pro- 
duced by  aggregations  of  brown  pigment  cells,  and  in  the 
colored  spots  on  the  elytra  of  many  coleopterous  insects,  as 
for  instance,  the  genus  coccinella,  which  is  specifically 
named  according  to  the  number  of  dark  spots  on  the 
scarlet  elytra.  All  the  endless  varieties  of  color  observable 
in  the  hair  of  animals,  in  the  plumage  of  birds,  and  on  the 
wings  of  lepidopfcerous  insects,  are  produced  by  aggrega- 
tions of  cells  which  contain  coloring  matter.  The  colors 
of  shells  result  from  the  same  cause.  Thus  one  and  the 
same  law  has  overspread  the  animal  and  vegetable  creation 
with  endlessly  diversified  hues. 

The  cells  of  the  animal  tissues,  exercise  the  same  select- 
ing power  as  the  cells  of  vegetables,  on  the  fluid  which  per- 
meates their  walls.  The  blood  is  laterally  transfused 
through  the  walls  of  the  capillaries,  and  its  constituents 
pass  in  a  molecular  form  through  the  parieties  of  the  cells 
contained  in  the  meshes  of  the  capillary  network;  each 
cell  acts  on  the  blood  in  its  own  peculiar  manner,  selecting 
its  own  proper  formative  material.  Thus  the  pigmentary 
cells  select  the  coloring  matter  of  the  blood,  rejecting 


COMPARED  WITH  THOSE  OP  ANIMALS.       45 

every  thing  else,  the  fat  cells  select  the  fatty  matters,  mus- 
cle produces  muscle,  bone  generates  bone,  nerve  developes 
nerve,  all  drawing  the  appropriate  materials  from  the  same 
fluid;  just  as  some  of  the  cells  of  plants  select  from  the  sap 
starch,  others  oils,  others  fluid  coloring  matters ;  or  as  the 
gelatinous  tissue  called  cambium,  interjacent  between  the 
bark  and  wood,  generates  during  the  season  of  vegetable 
growth,  beds  of  the  same  nature  as  those  with  which  it  is 
in  immediate  contact,  and  is  developed  into  ligneous  and 
cortical  fibre,  wood  producing  wood,  bark  forming  bark, 
the  tissues  preserving  their  cellular  organization  only  in 
those  portions  which  correspond  to  the  medullary  rays. 
Here  again  we  see  the  operation  of  the  same  laws  in  animal 
and  vegetable  matter. 

We  know  nothing  as  to  the  modus  operandi  of  the  pro- 
cesses in  the  cell-laboratory,  by  which  these  various 
organic  products  are  formed.  It  is  evident  that  they  are 
physiologically  connected  with  the  growth  of  the  other  parts 
of  the  organism  ;  for  the  vitality  of  all  the  organs  of  plants 
is  exhausted  in  succession,  in  developing  the  germ.  To 
this  tend  all  those  vital  changes  which  take  place  in  the 
cells  and  organs  of  plants  and  animals,  throughout  all  the 
ever  varying  phases  of  their  existence.  Here,  again,  we 
are  in  the  dark  as  to  the  physiological  uses  to  which  many 
of  the  various  products  of  the  cells  are  appropriated,  in  the 
animal  and  vegetable  economy.  Many  of  the  organic  pro- 
ducts of  plants  are  so  valuable  as  food  and  medicine  to  the 
animal  creation  and  to  man,  that  their  preparation  would 
appear  to  be  the  leading  function  of  the  plant,  and  the  grand 
reason  of  its  development. 

The  individuality  of  the  cells  of  organized  beings,  is  fur- 
ther proved  by  their  different  periods  of  life.  Many  of 
them  are  developed  only  to  serve  a  temporary  purpose, — 


46  THE  TISSUES  OF  PLANTS 

the  preparation  of  the  nutritive  material  for  the  more  per- 
manent parts  of  the  fabric, — this  purpose  being  accomplished, 
they  die  and  are  cast  off  from  the  organism  to  which  they 
are  of  no  further  use.  Thus  the  starch  cells  of  the  cotyle- 
dons perish  as  soon  as  the  first  pair  of  leaves,  to  whose 
nourishment  they  contribute,  are  capable  of  absorbing  the 
^nutritious  gases  of  the  atmosphere.  So  also  the  floral  appa- 
ratus fades  after  the  germ  is  fecundated.  Sometimes,  how- 
ever, after  the  corolla,  stamens,  and  the  upper  part  of  the 
pistil  have  perished,  the  vitality  of  the  calyx  remains  unim- 
paired j  and  seems  to  cooperate,  with  the  green  walls  of  the 
pericarp,  in  the  elaboration  of  those  juices  which  are  neces- 
sary to  the  growth  and  maturation  of  the  seeds  contained 
within  its  cavity.  In  the  Witch  Hazel,  Hamamelis  Vir- 
ginica,  the  vitality  of  the  leaves  is  exhausted  in  the  deve- 
lopment of  the  flowers,  which  do  not  appear  until  the  former 
decay  and  drop  from  the  branches.  The  massive  stem  of 
the  tree  is  fabricated  by  the  labors  of  the  successive  genera- 
tions of  leaves  with  which  it  was  annually  adorned.  The 
same  law  is  manifested  in  the  exuviation  of  the  epidermal 
appendages  of  the  body  of  the  inferior  animals,  such  as  hair, 
feathers,  teeth,  horns,  scales.  These  organs  are  thrown  off 
from  the  body  in  the  fall,  and  their  growth  renewed  in  the 
spring.  The  cells  which  form  them  have  evidently  a  life 
peculiar  to  themselves;  their  own  period  of  growth,  maturity, 
decay,  and  dissolution,  which  is  totally  different  from  that  of 
the  general  life  of  the  organism  with  which  they  are  con- 
nected. 

Thus  not  only  the  entire  plant  and  animal,  but  its  organs 
separately  and  individually  considered,  are  subject  to  certain 
definite  laws  of  development.  The  cells  of  animals  and 
plants  do  not  therefore  lose  their  individuality  by  being 
associated.  They  have  a,  life  of  their  own,  as  is  manifest 


COMPARED  WITH  THOSE  OF  ANIMALS.  47 

from  their  peculiarities  of  form,  their  secretions,  and  their 
different  periods  of  vital  activity.  There  appears  to  be  a 
division  of  organic  labor  among  them  and  a  relation  of 
mutual  dependency,  yet  each  contributes  in  its  own  way  to 
the  general  life  of  the  organism,  and  their  combined  action 
seems  to  be  absolutely  necessary  to  its  healthy  evolution 
from  the  seed,  spore,  or  ovum. 

We  have  endeavored  to  invite  the  attention  of  physiolo- 
gists to  the  fact  of  the  individuality  of  the  cells  of  plants 
and  animals.  There  can  be  little  doubt,  we  think,  that  the 
cells  of  all  organized  beings  are  subject  to  laws  of  develop- 
ment not  only  en  masse,  but  separately  and  individually 
considered.  As  yet,  however,  this  special  physiology  of  the 
cells  is  very  little  understood.  In  this  respect  we  believe 
vegetable  matter  to  be  peculiarly  instructive. 

ON  THE  CHEMICAL  COMPOSITION  OF  THE  VEGETABLE  AND 
ANIMAL  TISSUES. 

The  mucus  or  protoplasm  which  forms  the  nidus  of 
vegetation  and  animality,  is  formed  by  the  union  of  four 
simple  elementary  bodies,  Carbon  (C,)  Oxygen  (0,)  Hydro- 
gen (H,)  and  Nitrogen  (N.)  These  bodies  enter  the  organ- 
ism of  plants  chiefly  in  the  form  of  Carbonic  acid  (CO  2,) 
water  (HO,)  and  Ammonia  (NH  3,)  from  the  soil  and  atmos- 
phere, the  two  grand  sources  of  all  vegetable  nutrition. 
When  thus  united  they  are  called  binary  compounds.  Dex- 
trine, cellulose,  and  sugar  which  are  produced  by  the  union 
of  three  elementary  bodies,  viz.,  Carbon,  Hydrogen,  and 
Oxygen,  are  named  ternary  compounds;  and  fibrin,  albu- 
men, and  gelatin,  which  contain  Nitrogen  in  addition  to 
the  other  elements,  are  designated  as  quaternary  compounds. 

The  organic  compounds  resulting  from  the  union  of  these 
simple  elements  are  termed  proximate  principles.  They 


48  THE  TISSUES  OF  PLANTS 

may  for  the  most  part  be  obtained  by  very  simple  processes. 
Thus  if  water  be  added  to  flour  in  small  quantities,  a  duc- 
tile paste  will  be  formed  which, — when  kneaded  by  the 
hand  and  washed  by  a  slender  stream  of  water, — becomes 
a  grey,  tenacious,  and  highly  elastic  substance  termed  gluten. 
The  water  employed  in  this  process  is  rendered  turbid  and 
milky,  and  a  white  matter  remains  suspended  in  it,  which 
is  starch,  as  may  be  easily  ascertained  by  testing  it  with 
tincture  of  iodine.  So,  again,  when  meat  has  been  boiled 
for  some  time  in  water,  the  oil  is  observed  to  separate 
and  float  on  its  surface ;  but  another  substance,  separated 
from  the  meat,  remains  suspended  in  the  water,  which  soli- 
difies on  cooling.  This  substance  is  termed  gelatin.  The 
tasteless  shreds  which  remain  are  fibrin.  Now  gluten  and 
starch  are  instances  of  the  proximate  principles  of  plants; 
oil,  gelatin,  and  fibrin  are  examples  of  the  proximate  prin- 
ciples of  animals. 

The  walls  of  the  cells  or  elementary  parts  of  the  vegetable 
tissues,  are  not  formed  of  a  simple  homogeneous  substance, 
but  are  made  up  of  two  layers  of  very  different  composition 
and  properties.  The  innermost  layer,  which  is  the  mem- 
brane first  generated  over  the  nucleus,  has  for  this  reason 
been  called  the  primordial  utricle.  It  is  very  thin  and  deli- 
cate, and  escapes  attention  so  long  as  it  remains  in  contact 
with  the  outermost  layer,  from  which,  however,  it  is  easily 
detached  by  tincture  of  iodine.  To  the  primordial  utricle, 
all  the  subsequent  vital  operations  are  to  be  referred.  The 
external  layer  though  commonly  regarded  as  the  real  cell- 
wall,  is  in  reality  a  deposit  of  cellulose  which  is  generated 
on  the  outer  surface  of  the  primordial  utricle.  This  is  usu- 
ally thick  and  strong  compared  with  the  other,  and  pos- 
sesses various  degrees  of  consolidation,  from  the  condition  of 
mere  mucus,  to  a  firm,  tenacious,  and  elastic  substance. 


COMPARED  WITH  THOSE  OF  ANIMALS.  49 

* 

a  The  existence  of  the  primordial  utricle  in  a  normal  con- 
dition in  a  cell/'  says  Henfrey,  "  generally  indicates  that 
the  cell  still  retains  the  power  of  propagation,  and  it  is  con- 
sequently always  found  in  cambuim  cells."  The  primordial 
utricle  disappears  soon  after  the  commencement  of  the  for- 
mation of  the  secondary  layers  on  the  cell  wall. 

All  the  organs  of  plants  whatever  be  their  form,  their 
nature,  or  their  destination,  have  for  their  basis  the  same 
immediate  principle  cellulose,  which  when  deprived  of  all 
foreign  matter  and  brought  to  a  state  of  purity,  consists  of 
carbon  and  the  elements  of  water.  This  general  character, 
cellulose,  is  the  sign  of  the  vegetable  kingdom,  although 
the  rule  is  not  without  exceptions,  cellulose  having  been 
recently  detected  by  Schmidt,  Lowig,  and  Kolliker,  in 
the  tunics  of  ascidia  and  other  molluscous  animals. 

Cellulose  is  closely  allied  to  starch  in  its  chemical  com- 
position, but  differs  in  giving  a  yellow  in  place  of  a  blue 
color  with  iodine.  It  is  generally  colorless,  and  of  a 
whitish  hue ;  in  some  cases,  however,  as  in  ferns,  it  is 
brown.  When  thickened  by  successive  deposits,  it  pos- 
sesses a  laminated  structure.  It  is  readily  permeable  to 
fluids,  but  without  visible  pores. 

Plants  have,  therefore,  essentially  for  the  basis  of  their 
organization  a  ternary  matter  consisting  of  carbon,  oxy- 
gen, and  hydrogen,  "  which  exists  in  the  liquid  form  in  the 
state  of  vegetable  mucilage,  dextrine,  sugar,  &c.,  or  collects 
in  a  peculiar  solid  form  in  the  cells,  as  starch,  or  finally 
constitutes  the  proper  and  perinament  wall  of  the  cell, 
under  the  name  of  cellulose."*  Nitrogen  enters  sparingly 
into  the  composition  of  plants.  All  the  organs  of  plants, 
in  their  first  period  of  development,  contain  Nitrogen.  It 

*  See  Gray's  Botanical  Text-book,  p.  28. 


50  THE  TISSUES  OF  PLANTS 

exists  in  the  primordial  utricle  or  mucilaginous  lining  of 
all  young  and  growing  cells.  The  permanent  wall  of  the 
cell  is  formed  under  its  influence,  and  it  is  one  of  the  ele- 
ments of  vegetable  albumen,  fibrin,  caseine,  and  glutine, 
but  it  makes  no  part  of  the  permanent  frame-work  of  plants. 
Nitrogen,  on  the  other  hand,  enters  largely  into  the  com- 
position of  the  animal  tissues,  which  are  generally  quater- 
nary compounds,  consisting  of  carbon,  oxygen,  hydrogen, 
and  nitrogen. 


COMPARED  WITH  THOSE  OF  ANIMALS.  51 


CHAPTER  II. 

ON  THE  DEVELOPMENT  AND  PROPAGATION  OP  CELLS. 

So  far  as  we  at  present  know,  the  cell  like  the  plant,  is 
the  product  of  a  previously,  existing  cell.  Th9  principle 
omne  vivum  ex  ovo  is  applicable  to  vegetable  matter  under 
whatever  form  it  may  present  itself.  Life  is  only  known 
as  it  is  manifested  through  the  agency  of  cells,  and  the 
life-force  appears  to  be  generated  in  proportion  to  the 
extent  of  their  combination  and  the  development  of  their 
functions.  But  how  do  the  cells  of  plants  and  animals 
orginate  ?  Whence  come  those  new  utricles  which  without 
ceasing  are  added  to  those  already  in  existence,  and  which 
augment  incessantly  the  mass  from  whence  they  draw  their 
origin  ?  These  are  difficult  but  exceedingly  interesting 
questions. 

There  appear  to  be  three  principal  modes  in  which  cells 
are  multiplied,  viz.,  by  nuclei,  by  division,  and  by  gem- 
mation. 

1.   FORMATION  OF   CELLS  FROM  NUCLEI. 

According  to  Schleiden,  "  cells  can  only  be  formed  in 
a  fluid  which  contains  sugar,  dextrine,  and  proteine  com- 
pounds." They  originate  from  a  nucleus  or  cytoblast 
(xvtos  a  cell,  and  faaaibs  a  germ),  which  forms  either  in 
the  fluid  when  contained  in  the  cavity  of  a  pre-existing 
cell,  or  in  the  midst  of  it  when  effused  around  the  tissues 
of  growing  parts.  This  fluid, — to  which  the  terms  cam- 
bium, vegetable  mucilage,  and  protoplasm  have  been  ap- 


52  THE  TISSUES  OF  PLANTS. 

plied, — in  young  developing  organs  exists  *in  the  greatest 
abundance,  not  only  in  the  interior  of  their  cells,  but  also 
in  their  intercellular  spaces. 

M.  Mirbel,  to  whom  vegetable  anatomy  owes  so  many 
beautiful  discoveries,  believes  that  the  cytoblasts  form  in 
the  midst  of  the  fluid  which  fills  these  intercellular  spaces. 
He  gives  the  following  account  of  their  formation.  In  the 
points  where  the  new  cells  are  beginning  to  form,  we  see 
appear  small  gelatinous  globules.  This  is  the  commence- 
ment of  the  organization  of  the  fluid.  Very  soon,  each  of 
these  globules,  at  first  perfectly  transparent,  shows  a  little 
spot  slightly  opaque ;  this  results  from  the  formation  of 
a  cavity  in  its  interior,  and  we  have  a  globular  cell  formed 
which  is  the  second  degree  of  the  transformation  of  the 
nutritive  fluid.  This  cavity  dilates  itself,  the  walls  become 
more  and  more  transparent,  and  the  tissue  newly -formed 
finally  presents  the  same  characters  as  the  older  cells  with 
which  it  thus  becomes  associated. 

This  theory  of  Mirbel  has  been  opposed  by  many  phyto- 
tomists,  and  especially  in  Germany  by  linger  and  Mohl ; 
but  it  is  probably  true  with  reference  to  such  tissues  as  are 
swollen  and  succulent,  and  of  a  rapid  growth,  where  the 
cells  remain  loosely  aggregated,  and  retain  in  any  great 
measure  their  spherical  form. 

These  intercellular  spaces  exist  equally  in  the"  more 
dense  and  compact  tissues,  where  the  cells  become  angular 
and  polyhedral  by  mutual  pressure;  but  they  are  very 
much  reduced  in  size,  for  the  walls  of  the  contiguous  cel- 
lules in  this  instance,  touching  almost  completely  by  all 
their  points,  must  necessarily  render  these  spaces  almost 
imperceptible. 

These  views  of  Mirbel  have  been  in  some  measure  con- 
firmed by  the  researches  of  Schleiden;  and  as  his  ideas 


COMPARED  WITH  THOSE  OF  ANIMALS.  53 

applied  by  Swarm  to  the  tissues  of  animals,  are  now  ad- 
mitted by  almost  all  physiologists,  the  following  abridg- 
ment of  them  will  be  acceptable  : — 

When  there  are  the  appropriate  external  conditions,  the 
first  visible  stage  of  cell-formation  consists  in  the  appear- 
ance of  minute  granules  which  trouble  the  clear  gummy 
solution  in  the  cells,  or  the  interspaces  which  surround 
them,  rendering  it  turbid  and  opaque.  Some  of  these 
granules  collect  together  and  form  a  nucleus  around  which 
other  granules  (nudeoli)  gather,  so  that  they  ultimately 
acquire  a  larger  size  than  the  rest.  These  nucleated  agglo- 
merations, called  by  Schleiden,  cytoblasts,  become  each  an 
active  centre  around  which  the  mucilaginous  fluid  of  the 
protoplasm  organizes  itself.  As  soon  as  the  cytoblasts  are 
fully  grown,  a  fine  transparent  vesicle  developes  on  one 
side  of  them.  This  vesicle  first  appears  as  the  segment  of 

Fig.  11. 


Cells  of  a  leek,  after  Quekett.    a,  nucleus ;  &,  nucleolus. 

a  sphere,  the  cytoblast  forming  its  flat  side  and  the  walls 
of  the  vesicle  its  convex  surface..  The  vesicle  continues  to 
expand  until  at  length  the  cytoblast  from  which  it  ori- 


54 


THE  TISSUES  OF  PLANTS 


ginated,  appears  but  as  a  small  opaque  body,  which  is  either 
centrally  located,  or  attached  to  one  of  its  walls. 

Thus,  according  to  Schleiden,  the  cytoblast  or  nucleus 
visible  in  the  cellule,  has  originated  the  cellule  itself.  It 
is  seldom,  however,  that  the  cytoblast  remains  visible  for 
any  length  of  time  after  the  cell  has  been  fully  formed; 
generally,  it  is  re-absorbed. 

The  cytoblast  is  beautifully  apparent  in  the  moniliform 
hairs  of  Tradescantia.  Virginica, 

The  elementary  cells  which  compose  the  tissues  of  ani- 
mals also  contain  these  nuclei  or  cytoblasts. 

Fig.  12. 


Nucleated  cartilage  cells  from  the  Chorda  dorsalis  of  a  Lamprey. 

Of  this  we  have  a  very  beautiful  and  striking'  proof 
afforded  in  the  above  engraving.  The  Chorda  dorsalis  is 
an  extremely  thin  and  delicate  tube,  composed  of  cells  in 
close  opposition  with  each  other,  and  enclosing  the  spinal 
chord.  It  is,  in  fact,  the  vertebral  column  arrested  in  the 
first  stage  of  its  development.  This  is  its  permanent  con- 
dition in  the  lamprey,  and  also  in  the  lowest  group  of  car- 
tilaginous fishes. 


COMPARED  WITH  THOSE  OF  ANIMALS.  55 

2.  FORMATION  or  CELLS  BY  DIVISION. 

This  mode  of  cell-multiplication  is  probably  that  which 
presents  itself  most  frequently  to  the  observer.  It  may 
be  studied  to  the  greatest  advantage  in  that  common  green 
thread-like  vegetation  known  to  botanists  as  Confervas, 
which  is  found  in  the  beds  of  rivulets  attached  to  their 
stones  and  pebbles,  and  which  invariably  shows  itself  on 
the  surface  of  rocks  whenever  the  water  which  flows  over 
them  is  exposed  to  the  action  of  light.  This  matter,  ex- 
amined with  the  microscope,  presents  to  the  eye  a.  longi- 
tudinal series  of  cells  which  are  produced  by  merismatic 
division  in  the  following  manner : — 

The  primordial  utricle  or  inner  wall  of  the  cell  is  in- 
flected towards  its  middle  part.  This  inflection,  at  first 
a  little  salient,  insensibly  increases  until  finally  the  two  in- 
flected walls  meet  in  the  centre  of  the  cell,  and  form  a 
complete  partition  across  its  cavity,  so  that  in  the  place  of 
one  we  have  two  cells.  These  dilate  and  subdivide  again 
in  the  same  manner,  and  in  this  way  a  linear  series  of  cells 
is  produced,  when  the  subdivision  of  them  takes  place  in 
one  direction,  or  a  plane  or  solid  mass  of  cells  when  it 
takes  place  in  two  or  more  directions.  The  endochrome  of 
the  primary  cell,  is  necessarily  separated  into  two  halves  by 
the  formation  of  the  septum,  and  is  again  subdivided  with 
every  repetition  of  the  process,  so  that  all  the  cells  contain 
a  separate  portion  of  it.  The  contiguity  of  the  cells  blends 
together  the  hues  of  their  separate  endoch'romes,  and  gives 
an  evenly  diffused  color  to  the  surface  of  the  tissues. 

These  fresh  water  confervas  illustrate  the  vegetative  pro- 
cess in  more  highly  organized  plants,  which  acquire  their 
complex  structure  from  equally  simple  beginnings.  Hence 
it  is  not  original  cell-formation  so  much  as  the  multiplica- 


56 


THE  TISSUES  OF  PLANTS 


tion  of  cells  already  existing,  which  causes  growth  or  the 
extension  of  the  parts  of  plants.  In  this  respect  precisely, 
the  same  laws  operate  in  plants  composed  of  a  single  row 
of  cells,  as  when  nature  works  on  a  more  enlarged  scale. 
The  most  important  physiological  truths  may  therefore  be 
learned  from  vegetation  apparently  insignificant.  "  Natura 
wnwiis 

Fig.  13. 


Branching  summit  of  a  fresh  water  plant,  Conferva  glomerata,  magnified, 
showing  at  upper  a,  the  partitions  forming  by  the  infolding  process,  and  at 
lower  a,  the  partitions  complete. 

*  Linnaeus. 


COMPARED  WITH  THOSE  OF  ANIMALS.  57 

The  multiplication  of  cells  by  division  is  common 
among  the  infusoria,  which  increase  by  what  is  called  the 
fissiparous  method  of  reproduction,  in  a  manner  precisely 
analogous  to  the  mode  of  increase  among  the  parallel  group 
of  plants.  The  parenchyma  of  the  cell  at  first  becomes 
more  opaque,  a  clear  line  is  seen  to  form  across  its  cavity, 
and  a  sort  of  hour-glass  contraction  takes  place  along  this 
line.  Each  division  now  struggles  to  separate  from  its 
fellow,  and  the  separation  is  no  sooner  effected  than  the 
two  cells  dart  off  in  opposite  directions,  and  rapidly  assume 
their  normal  size  and  figure.  This  division  sometimes 
takes  place  vertically,  as  in  vorticella,  and  sometimes  trans- 
versely. In  some  of  the  infusoria,  the  Paramecia,  for  in- 
stance, it  occurs  as  often  as  three  or  four  times  a  day. 

The  multiplication  of  cells  by  division,  is  beautifully  ap- 
parent in  the  development  of  cells  within  the  mammalian 
ovum,  which  has  especially  a  plant-like  mode  of  growth. 
The  ova  of  all  the  different  orders  of  the  vertebrata,  birds, 
fishes,  reptiles,  as  well  as  mammalia,  have  in  the  beginning 
nearly  the  same  uniform  structure;  and  although  it  is  by 
differences  in  the  processes  of  cell-multiplication  whilst  in 
•the  embryonic  condition,  that  those  differences  which  cha- 
racterize the  full-grown  animals  are  brought  about,  yet  the 
principle  of  division  is  in  all  ova  precisely  the  same.  The 
process  has  been  observed  in  the  impregnated  ovum  of 
Ascaris  acuminata,  one  of  the  oviparous  Entozoa,  which  is 
a  very  favorable  subject  for  the  study  of  it,  owing  to  the 
transparency  of  its  body,  and  it  is  found  that  the  embryonic 
mass  commences  very  much  after  the  same  plan  as  in  plants. 
Fig.  14  shows  the  successive  stages  of  segmentation.  The 
ovum  having  been  impregnated,  the  yolk-bag  slightly  sepa- 
rates from  the  enveloping  membrane  and  subdivides  into 
two  halves,  each  of  these  again  subdivides  into  two  more, 


58  THE  TISSUES  OF  PLANTS 

and  so  on;  so  that  in  place  of  one  cell  we  have  2,  then  4,  8, 
16,  32,  64,  until  the  whole  yolk  assumes  a  mulberry-like 
appearance.  The  cells  now  begin  to  manifest  their  individu- 
ality, and  gradually  develope  into  the  form  of  the  future 
worm. 

Fig.  14. 


Successives  stages  of  segmentation,  in  the  vitellus  of  the  ovum  of  Ascaris  acu- 
minata.  A,  recently  impregnated  ovum,  with  yolk-bag  slightly  separated 
from  the  enveloping  membrane ;  B,  first  fission  into  two  halves ;  C,  second  fission 
forming  four  segments ;  D,  E,  and  P,  formation  of  mulberry  mass  by  further  seg- 
mentation ;  G,  the  mass  of  cells  showing  the  form  of  the  future  worm ;  H,  the 
worm  formed  by  the  conversion  of  the  yolk-cells,  now  nearly*  mature. — CAR- 
PENTER. 

In  most  of  the  animal  tissues  the  multiplication  of 
cells  by  division  takes  place  during  the  embryonic  state  of 
development,  but  in  some  cartilages  it  appears  to  take  place 
throughout  the  whole  period  of  their  life.  Most  of  the 
articular  cartilages  which  cover  the  ends  of  the  bones  retain 
their  primitive  cellular  organization,  which  may  be  seen  at 
any  time.  Fig.  15  shows  the  successive  steps  in  the  mul- 
tiplication of  cartilage  cells.  In  this  process,  as  in  all  the 
other  acts  of  cell-life  in  animals,  the  nucleus  seems  gene- 
rally to  take  a  more  conspicuous  part  than  it  does  in  plants. 


COMPARED  WITH  THOSE  OF  ANIMALS. 


59 


Thus  as  soon  as  the  first  inflection  can  be  traced  in  the 
walls  of  the  cell,  the  nucleus  begins  to  undergo  subdivi- 
sion, and  when  the  cell  is  finally  divided,  each  cavity  con- 
tains a  portion  of  the  nucleus.  These  two  new  cells  with 
their  contained  nuclei  again  subdivide  in  a  similar  manner, 


Development  of  cartilage  cells.  A,  original  cell;  B,  the  same  beginning  to 
divide ;  C,  the  same,  showing  complete  division  of  the  nucleus ;  F,  the  same  with, 
the  halves  of  the  nucleus  separated ;  G,  and  H,  continuation  of  the  same  pro- 
cess; by  continued  cleavage  in  the  same  direction,  and  the  ultimate  produc- 
tion of  a  longitudinal  series  of  cells.— CARPENTER. 

producing  a  filament  or  row  of  cells,  when  the  division  takes 
place  in  one  direction,  and  a  plane  or  solid  mass  of  them, 
when  the  cleavage  takes  place  in  two  or  more  directions. 

3.  FORMATION  OF  CELLS  BY  GEMMATION  OR  BUDDING. 

This  is  well  seen  in  Conferva  glomerata,  Fig.  13,  which  in- 
creases, not  only  longitudinally  by  the  repeated  subdivision 
and  expansion  of  the  cells  at  the  extremity  of  its  filaments, 
but  laterally  by  a  process  of  outgrowth  or  budding.  A  cer- 


60  THE  TISSUES  OF  PLANTS 

tain  portion  of  the  cell-wall  seems  to  undergo  an  increased 
nutrition,  so  that  it  gradually  forms  an  outward  swelling  or 
protuberance ;  the  primordial  utricle,  or  inner  wall  of  the 
lateral  cellule  thus  formed,  is  inflected,  as  in  the  preceding 
case,  and  a  septum  organizes  across  its  cavity,  by  which  it  is 
completely  separated  from  the  parent  cellule ;  after  which, 
the  multiplication  and  further  enlargement  of  the  cells  in 
this  direction  takes  place  by  the  ordinary  methods  of 
division. 

We  have  as  yet  no  certain  knowledge  as  to  the  extent  to 
which  this  budding  process  takes  place  in  plants.  It  is 
clearly  the  regular  mode  of  growth  among  the  Characece. 
The  long,  tubiform,  and  articulated  cells  which  form  the 
axis  of  these  plants,  give  off  at  their  points  of  junction 
with  each  other,  a  circular  row  of  buds,  which  ultimately 
become  elongated  into  a  verticil  of  branches.  It  is  pro- 
bable that  this  process  of  gemmation  or  budding  is  the  same, 
in  principle,  as  that  which  causes  all  lateral  growth  in  plants. 
The  symmetrical  arrangement  of  the  leaves,  buds  and 
branches,  proves  that  they  are  subjected  to  definite  laws 
of  development,  and  they  must  therefore  necessarily  origi- 
nate in  certain  definite  cells  which  have  a  tendency  to  de- 
velope  laterally,  and  appear  to  be  specialized  or  set  apart 
from  the  rest  for  that  very  purpose.  The  process  of  divi- 
sion as  seen  in  the  longitudinal  development  of  the  cells 
of  Conferva  glomerata,  is  identical  with  the  ordinary  modes 
of  longitudinal  increase  in  all  the  young  and  growing  parts 
of  plants ;  and  the  process  of  gemmation  as  seen  in  the 
lateral  development  of  the  cells  of  the  same  plant,  would 
seem  to  be  only  a  simplified  expression  of  that  same  law 
which,- in  the  more  elaborate  productions  of  nature,  mani- 
fests itself  in  the  formation  of  the  buds,  branches,  leaves 
and  other  appendages  of  the  vegetable  axis. 


COMPARED  WITH  THOSE  OF  ANIMALS.  61 

The  multiplication  of  cells  by  gemmation  or  buddmg, 
and  also  by  division,  is  seen  in  animals  as  well  as  plants,  in 
the  simplest  as  well  as  the  most  complex  forms.  Thus  the 
whole  zoophytic  structure  is  produced  by  continuous  gem- 
mation from  a  single  ovum,  and  in  the  lower  articulata, 
annelida,  and  reptilia,  the  parts  of  the  body  which  have 
been  accidentally  lost  are  speedily  reproduced.  It  is  well 
known  that  crabs  and  spiders,  on  losing  a  limb,  acquire  a 
new  one.  The  same  happens  with  the  arms  of  star-fishes. 
The  tail  of  a  lizard  is  also  reproduced.  Salamanders  re- 
cover their  lost  legs,  and  even  the  eye,  with  all  its  com- 
plicated parts.  These  vegetative  manifestations  are,  how- 
ever, mainly  restricted  to  the  lower  forms  of  the  animal 
kingdom ;  as  animal  life  becomes  more  developed,  this  repa- 
rative  power  is  proportionably  lessened,  although  we  are 
not  without  some  evidence  of  it  in  our  own  bodies,  as  when 
a  new  skin  is  formed  over  a  wound,  or  a  broken  bone  is  re- 
united. 


62  THE  TISSUES  OP  PLANTS 

CHAPTER  III. 

ON  THE  TRANSFORMATION  OF  CELLS  INTO  TISSUES. 

We  have  already  given  some  examples  of  this  transfor- 
mation of  cells  in  plants,  and  have  shown  that  it  takes  place 
to  a  much  greater  .extent  in  the  animal  tissues.  Some 
additional  remarks  are  however  necessary,  in  order  to  bring 
this  subject  fully  before  the  reader. 

Cellulose  is  at  first  an  exceedingly  tough,  transparent, 
thin,  and  elastic  substance,  which  may  be  compressed  or  ex- 
tended into  any  shape  whatever.  Its  impassive  and  yield- 
ing nature  is  exemplified  in  the  innumerable  varieties  of 
shape  assumed  by  the  cellsx  As  the  earthy  matter  is 
deposited  on  the  interior  parietes  of  the  cells,  it  gradually 
acquires  rigidity  and  firmness. 

Whilst  in  the  embryonic  condition,  the  woody  and  fibro- 
vascular  portions  of  plants  are  not  to  be  distinguished  from 
the .  ordinary  cellular  tissue.  The  vasculares,  or  most 
highly  developed  of  the  flowering  plants,  are  at  first  as  low 
in  organization  as  the  cellulares  or  flowerless  plants.  This, 
however,  is  with  them  but  a  transient  stage  of  existence. 
As  soon  as  active  life  commences  in  the  seed,  the  cells 
begin  to  manifest  their  individuality,  and  each  to  perform 
its  peculiar  part  in  the  building  up  of  the  organism.  Some 
of  them  become  rapidly  elongated  into  fibres,  others 
coalesce  into  tubes,  and  the  nutrient  fluid  which  at  first 
equally  pervaded  all  parts  of  the  organism,  necessarily  .sets 
in  a  current  through  the  vascular  and  fibrous  tissue,  owing 
to  their  tubular  and  capillary  structure. 

Now  the  water  which  enters  the  roots  of  plants  from  the 


COMPARED  WITH  THOSE  OP  ANIMALS.  63 

soil,  is  impregnated  with  various  earthy  matters  necessary 
to  the  health  and  life  of  the  plant.  These  earthy  matters 
are  deposited  in  the  cells  of  plants  from  the  very  com- 
mencement of  their  growth,  but  not  to  any  great  extent 
until  they  have  acquired  their  full  development.  As  the 
secondary  deposit  forms  on  the  cell  walls,  the  cells  acquire 
rigidity,  and  growth  is  therefore  necessarily  arrested. 

It  has  been  shown  that  the  fibro-vascular  system  of 
plants  is  subordinate  in  function  to  the  cells  of  the 
parenchyma,  and  that  it  subserves  the  simple  physical  pur- 
pose of  conveying  to  them  the  nutrient  fluid  or  sap.  The 
fibro-vascular  system  of  the  stem  terminates  in  the  leaves, 
where  it  takes  a  horizontal  spread,  and  is  attenuated  into 
a  plexus  or  network  of  capillaries,  which  anastomose  with 
each  other  in  the  same  manner  as  the  capillary  vessels  in 
man. 

The  design  of  nature  in  forming  the  leaves  of  plants,  is 
to  spread  the  fluid  over  a  horizontal  surface,  so  that  it  may 
be  the  more  readily  exposed  to  the  air  and  light.  The 
anatomical  structure  of  the  leaf  proves  this.  The  leaves  of 
plants  are  simply  horizontal  expansions  of  the  fibro-vascular 
and  cellular  tissues  of  the  wood  and  bark  of  the  stem,  with 
which  every  part  of  the  leaf  directly  communicates.  The 
sap  appears  to  be  transferred  laterally  through  the  walls  of 
the  capillaries,  and  to  be  imbibed  by  the  parieties  of  the 
parenchymatous  cells  amongst  the  meshes  of  the  capillary 
network.  It  is  in  the  leaves  then  that  the  principal 
changes  in  the  sap  take  place. 

Now  the  current  of  sap  is  kept  continually  flowing 
through  the  fibro-vascular  portions  of  the  stem,  owing  to  < 

the  constant  evaporation  which  is  going  on  at  the  surface 
of  the  leaves.  Earthy  matter  is  therefore  necessarily 
rapidly  accumulated  in  those  cells  through  which  the  fluid 


64  THE  TISSUES  OF  PLANTS 

is  transmitted.  In  some  instances  it  is  deposited  concen- 
trically, as  for  example,  in  the  fibrous  portion  of  the  wood, 
and  it  goes  on  accumulating  until  the  tubular  character  of 
the  fibre  cells  is  wholly  obliterated. 

In  the  different  varieties  of  vasiform  tissue  and  ducts,  the 
tubular  character  of  the  tissue  permanently  remains. 
These  vessels  originate  from  the  union  or  confluence  of 
porous,  rayed,  annular,  and  spiral  cells. 

Tj^prft  appears  to  be  a  tendency  in  the  secondary  deposit 
to  arrange  itself  spirally  on  the  inner  parietes  of  the  duct- 
cells.  In  some  instances  the  spiral  is  perfectly  formed, 
its  several  coils  lying  close  together  in  the  vessel  and  ad- 
hering firmly  to  its  walls.  When,  therefore,  the  vessel  is 
raptured,  its  membrane  tears  in  the  direction  of  the  turns 
of  the  spiral,  with  which  it  is  ultimately  united  and  from 
which  it  cannot  be  distinguished ;  but  when  the  turns  of 
the  spiral  are  more  or  less  separated  fr«im  each  other  by 
the  elongation  of  the  vessel,  its  walls  are  apparent  between 
the  several  coils,  and  the  existence  of  the  spiral  fibre  within 
its  cavity  is  at  once  demonstrated. 

Whilst  the  coils  of  the  spiral  lie  close  together  in  the 
cell,  they  are  very  apt  to  anastomose.  Sometimes  several 
of  the  fibres  will  unite  throughout  their  entire  extent  and 
produce  a  banded  spiral.  This  disposition  is  frequent  in 
monocotyledonous  plants,  particularly  in  the  banana.  Fre- 
quently the  anastomosis  between  two  or  more  turns  of  the 
fibre  is  only  partial,  and  in  this  way  the  so-called  reticulated 
spiral  fibre  is  probably  produced.  Itt  some  cases,  aS  the 
cell  elongates,  the  fibre  breaks  up  into  a  series  of  rings, 
and  annular  vessels  are  the  result.  This  form  of  the  spiral 
fibre  is  common  in  monocotyledons.  In  place  of  rings,  the 
fibre  may  separate  at  regular  intervals  and  form  bars,  or 
may  be  even  so  broken  up  as  to  appear  in  the  form  of  dots 


COMPARED  WITH  THOSE  OF  ANIMALS.  65 

or  opaque  points  on  the  cell  wall.  The  scalariform  and 
porous  varieties  of  ducts  are  thus  generated.  That  all 
these  differences  in  the  fibro-vascular  tissue  are  only  modi- 
fied forms  of  the  spiral  deposit,  is  proved  by  the  occasional 
presence  of  the  spiral,  the  annular,  the  scalariform,  and 
even  the  dotted  varieties  of  deposit  in  the  same  vessel. 

The  porous  or  dotted  cells  which  form  the  tubular  tissues 
termed  by  botanists  bothrenchyma,  are  not,  however,  re- 
ferable to  the  fibrous  type,  from  which  they  differ  totally 
in  their  original  formation.  These  cells  are  endowed  with 
the  peculiar  property  of  restricting  the  earthy  deposit  to 
certain  portions  of  their  parietes ;  the  thickening  process 
continues  at  these  points,  the  other  parts  of  the  cell-wall 
remaining  uncovered.  The  dotted  appearance  of  the  cell- 
wall  results  therefore  in  this  case,  not  from  the  presence 
of  an  opaque  deposit,  but  from  its  absence.  The  pits,  or 
cavities  of  contiguous  cells,  frequently  correspond  with  each 
other  notwithstanding  the  thickening  of  their  walls,  as  is 
clearly  shown  in  the  wood  of  the  American  plane  tree. 
These  facts  prove  that  the  earthy  matter  is  controlled  in  its 
deposition  on  the  cell-wall,  by  other  influences  than  those 
which  are  purely  mechanical,  and  that  the  phenomena  is 
to  be  attributed  to  a  peculiar  vital  action,  originating  in 
the  individuality  of  the  cells. 

To  the  same  cause  is  to  be  attributed,  the  different 
varieties  of  canaliculi  or  radiating  tubes  in  the  more  indu- 
rated deposits,  termed  sclerogeu.  The  stony  envelope 
which  surrounds  the  seeds  of  the  peach  and  plum,  together 
with  the  shell  covering  of  nuts  and  filberts  may,  in  this  re- 
spect, be  fairly  contrasted  with  the  more  solid  and  indurated 
tissues  of  animals.  Bone,  for  example,  exhibits  the  same 
lacunae,  canaliculi,  and  radiating  processes,  amongst  other 
peculiarities,  "In  the  Histological  Catalogue  of  the 
6* 


66  THE  TISSUES  OF  PLANTS 

Museum  of  the  College  of  Surgeons,  London,  all  the  prin- 
cipal varieties  of  the  deposit  of  sclerogen  are  classified  and 
described  under  the  name  of  hard  tissues,  and  contrasted 
with  bone  and  teeth  which  form  the  hard  tissues  of 
animals."* 

Earthy  deposits  sometimes  occur  in  the  cells  of  plants 
in  the  form  of  crystals  or  raphides.  These  consist  of  inor- 
ganic matter,  generally  of  some  acid  and  its  base,  which 

Fig.  16. 


A  portion  of  the  outer  layer  of  the  bulb  of  Scitta  maritima,  having  aeicular 
.rapMdes  in  some  of  its  cells. 

has  united  and  crystallized  in  the  cells.  There  is  nothing 
surprising  in  the  existence  of  these  crystals.  We  know 
that  acids  are  formed  in  the  vegetable  organs,  and  these 
unite  with  the  earths  or  bases  taken  up  by  the  roots  from 
the  soil,  whilst  they  are  suspended  in  the  cell-sap.  These 

*  "  Lectures  on  Histology,  delivered  at  the  Royal  College  of  Sur- 
geons of  England,  in  the  session  1850-51,  by  John  Quekett.   1852." 


COMPARED  WITH  THOSE  OF  ANIMALS. 


67 


crystals  are  of  different  sizes  and  forms,  rhomboidal,  cubi- 
cal, and  prismatic ;  but  the  most  prevalent  figure  is  the 
acicular  and  needle-shaped.  They  occur  either  singly  or 
in  stellate  masses.  The  stellate  figure  is  generally  assumed 
by  the  acicular  and  prismatic  varieties,  to  which  the  term 
raphides  (ports'*  a  needle,)  was  originally  applied  by  Decan- 
dolle,  although  it  is  now  used  indiscriminately  in  reference 
to  all  cellular  crystals.  These  crystals  occur  in  all  parts  of 
the  plant,  in  the  stem,  bark,  leaves,  petals,  and  root ;  they 
usually  consist  of  the  oxalic,  carbonic,  malic,  phosphoric, 
citric,  and  other  organic  acids  united  to  lime  as  a  base. 
The  octohedral  variety  may  be  readily  seen  in  the  cuticular 
cells  of  the  bulb  of  the  onion.  Acicular  crystals  may  be 
procured  from  the  petiole  of  Calla  Ethiopica,  by  making  a 
section  and  spreading  the  mucilaginous  contents  of  the 
cells  over  the  field  of  the  microscope. 

The  adipose  tissue  of  old  persons  sometimes  contains 
acicular  crystals.  Fat  consists  of  a  liquid  and  solid  prin- 
ciple, the  former  is  termed  elaine,  the  latter  margarine. 
These  acicular  crystals  are  the  solid  element  or  margarine 
which  has  separated  from  the  elaine. 


Fig.  17. 


Adipose  cells,  each  containing  needle-shaped  crystals  of  margarine. 


68  THE  TISSUES  OF  PLANTS 

Fig.  17,  is  a  specimen  of  adipose  tissue  from  a  female 
seventy  years  of  age.  Each  cell  contains  a  stellate  mass 
of  needle-shaped  crystals.* 

The  vasiform  tissue  and  ducts  in  early  spring,  when  the 
ascent  of  the  sap  is  most  powerful,  at  first  convey  it  to  the 
leaves  in  conjunction  with  the  fibre-cells  of  the  wood.  But 
as  the  flow  of  the  sap  becomes  less  vigorous,  it  gradually 
disappears  from  the  ducts  and  spiral  vessels,  owing  to  their 
deficiency  in  the  requisite  amount  of  capillarity,  which  thus 
become  filled  with  air.  In  this  second  period  of  vegetation 
they  become  organs  of  respiration,  and  as  they  are  spread 
through  the  interior  of  the  stem  and  enter  the  leaves  through 
their  foot-stalks,  communicating  with  the  intercellular  spaces 
amongst  the  cells  of  their  parenchyma,  and  with  the  pores 
on  their  outer  surface ;  the  sap  in  the  interior  of  the  plant 
is  thus  brought,  through  their  agency,  into  constant  commu- 
nication with  the  nutritious  gases  of  the  atmosphere. 

As  the  sap  very  soon  retires  from  the  vasiform  tissue 
and  ducts,  the  earthy  deposits  on  their  parieties  do  not  take 
place  to  any  very  great  extent,  and  hence  they  retain  their 
tubular  character  throughout  the  life  of  the  plant.  As 
the  force  of  the  ascending  current  diminishes,  it  forsakes 
the  large  capillaries  of  the  fibro-vascular  tissue ;  for  the  same 
reason,  its  flow  through  the  finer  capillary  tubes  of  the  fibre- 
cells  continues,  after  its  flow  in  the  fibro-vascular  system 
ceases.  Hence  earthy  matter  goes  on  accumulating  in  the 
fibre-cells,  until  it  ultimately  fills  up  their  cavities,  and  ob- 
literates their  tubular  character.  When  this  is  the  case, 
their  vital  activity  ceases,  and  they  exercise  a  purely 
mechanical  function.  To  the  deposits  of  earthy  matter  in 
the  fibre  cells  of  the  wood,  the  term  lignine  is  applied;  in 

*  "  Lectures  on  Histology,  &c.,"  by  John  Quekett.  p.  187. 


COMPARED  WITH  THOSE  OP  ANIMALS.  69 

order  to  distinguish  them  from  those  earthy  accumulations 
celled  sclerogen,  which  produce  the  more  indurated  tissues 
investing  the  seeds  of  plants.  The  strength  of  the  stem 
and  root  depends  on  the  lignine  accumulated  in  the  fibrous 
portion  of  their  tissues ;  and  the  fibrous  tissues,  thus  solidi- 
fied, constitute  the  skeleton  or  frame-work  of  the  plant. 

In  the  same  manner,  earthy  matter  accumulates  more 
rapidly  in  some  of  the  tissues  of  the  animal  body  than  in 
others  ;  in  bone  for  instance,  which  thus  becomes  solid  and 
hard,  and  peculiarly  fitted  to  support  the  softer  part  of  the 
animal  frame  work.  Like  the  ligneous  system  of  plants,  the 
osseous  system  of  animals  is  the  last  to  arrive  at  maturity, 
the  process  of  ossification  in  the  human  skeleton  not  being 
complete  until  about  the  16th  or  18th  year.  The  time  of 
its  commencement  and  completion,  varies  in  different  parts 
of  the  skeleton.  The  bones  first  formed  are  those  which 
enclose  the  central  organs  of  circulation  and  the  nervous 
system.  The  ossification  of  the  extremities  takes  place  at 
a  later  period. 

Bone  is  composed  of  animal  and  earthy  matter,  the 
former  consists  of  gelatine,  the  latter  of  phosphate  of  lime. 
If  bone  be  burnt  in  a  clear  fire  for  about  fifteen  minutes, 
the  animal  matter  is  destroyed,  and  the  earthy  matter 
remains  as  a  white  and  brittle  substance,  the  bone  retaining 
its  form ;  on  the  other  hand,  if  bone  be  digested  in  mu- 
riatic acid  for  a  few  days,  the  earthy  matter  is  entirely  re- 
moved, and  the  animal  matter  remains,  as  a  tough  elastic 
substance,  which  can  be  bent  in  any  direction. 

In  childhood  and  youth  the  animal  matter  preponderates 
over  the  earthy.  The  gelatinous  and  flexible  bones  of  the 
extremities  of  a  child  curve  outwardly  from  this  cause,  as 
they  are  too  weak  to  support  the  weight  of  its  body,  and 
sometimes  become  permanently  deformed  if  the  child  is 


70  THE  TISSUES  OF  PLANTS 

neglected.  As  childhood  ripens  into  youth,  earthy  matter 
is  deposited  in  the  bones,  they  acquire  rigidity  and  firmness, 
and  the  extremities  straighten.  In  manhood,  their  strength 
has  arrived  at  its  maximum  development,  and  they  are 
most  admirably  adapted,  not  only  to  support  the  softer  parts 
of  the  body,  but  to  serve  as  a  basis  for  the  attachment  of 
the  muscles  which  execute  its  movements.  As  we  advance 
in  years,  the  vitality  of  the  bones  diminishes,  and  in  old 
age  they  become  extremely  brittle,  owing  to  the  great  pre- 
ponderance of  the  phosphate  of  lime  over  the  gelatine. 

The  blood  vessels  of  animals  appear  to  be  formed  like 
the  ducts  of  plants,  by  the  coalescence  of  cells  arranged  in 
a  linear  series.  In  both  the  ducts  and  blood-vessels,  the 
organs  remain  permanently  open ;  but,  whilst  the  flow  of  the 
nutrient  fluid  speedily  subsides  in  the  one,  it  continues  in 
the  other  as  long  as  life  remains.  Again,  all  the  different 
varieties  of  vasiform  tissue  or  ducts,  are  distinguished  by 
their  want  of  any  tendency  to  branch  or  anastomose.  It ,is 
the  function  of  these  ducts  to  convey  fluids  and  air  in  the 
most  direct  manner  possible,  from  [one  extremity  of  the 
plant  to  the  other,  and  therefore  they  run  in  parallel  lines 
through  the  stem  and  its  branches;  and,  as  they  are  sur- 
rounded by  a  sheath  of  woody  fibre,  they  can  have  little  or 
no  lateral  communication  until  they  enter  the  leaves,  where 
the  woody  fibre  is  spread  horizontally.  But  the  organiza- 
tion of  the  animal  body  is  such,  as  to  require  that  the  blood- 
vessels should  be  distributed  from  the  very  first  on  the 
ramifying  principle.  Accordingly,  those  which  convey 
blood  to  any  part,  progressively  divide  and  subdivide, 
diverging  from  each  other  like  the  branches  of  a  tree  from 
its  trunk,  and  their  several  divisions  divide  and  subdivide, 
again  forming  branchlets ;  this  process  of  division  and  sub- 
division is  continued,  until  the  arterial  tubes  finally  ter- 


COMPARED  WITH  THOSE  OP  ANIMALS.  71 

minate  in  a  network  of  anastomosing  capillaries  like  those 
in  the  leaves  of  plants,  by  means  of  which  the  blood  is  dis- 
tributed to  all  parts  of  the  organ. 

These  capillaries  not  only  cover  the  surface  of  the  body 
and  all  its  organs,  but  they  penetrate  their  substance,  con- 
veying the  blood  to  every  part  of  the  fabric.  The  capillary 
system  is  interjacent  between  the  venous  and  arterial  sys- 
tems. It  is  in  traversing  these  capillaries  that  the  blood 
changes  from  scarlet  to  purple,  in  consequence  of  giving  up 
its  nutrient  principles  to  the  tissues. 

The  blood  leaves  these  capillaries  by  means  of  the  veins, 
each  of  which  is  first  formed  by  the  union  of  several  capil- 
laries; these  collect  and  return  the  blood  after  it  has 
traversed  the  organs  of  the  body,  converge  and  reunite  into' 
larger  and  larger  vessels,  like  the  roots  of  a  tree  or  the 
sources  of  a  river.  In  this  manner  the  blood  is  again 
brought  back  to  its  original  source,  the  heart,  from  whence 
it  is  driven  into  the  lungs.  There  the  fluid  is  brought  into 
immediate  contact  with  the  atmospheric  air  absorbed  during 
respiration,  is  oxygenated,  and  again  returned  to  the  heart, 
from  whence  it  is  again  driven  into  the  aorta,  and  conveyed 
by  its  ramifications  as  before,  to  all  parts  of  the  body. 

Whilst  therefore  in  plants  the  capillary  system  is  con- 
fined to  the  leaves,  in  animals  it  pervades  every  part  of  the 
body.  The  capillary  system  of  plants  is  only  required 
during  the  season  of  vegetable  activity,  and  is  not  needed 
during  the  period  of  vegetable  repose.  The  leaves  are 
therefore  only  temporary  organs,  and  the  plant  loses  its 
capillaries  when  it  becomes  defoliated.  The  woody  fasci- 
culi which  form  the  newly  developed  shoots  at  the  extremi- 
ties of  the  branches  alone  remain,  permanently  attached  to 
the  plant,  together  with  the  dormant  buds  on  their  exterior 
surface.  It  is  through  the  influence  of  the  leaves  with 


72  THE  TISSUES  OF  PLANTS 

which  it  is  temporarily  adorned,  that  the  more  permanent 
parts,  the  stem  and  branches,  are  enabled  to  increase  in 
size  from  year  to  year.  There  in  no  such  cessation  to 
growth  and  vital  activity  in  the  animal  body ;  hence  the  ca- 
pillaries form  permanent  parts  of  the  fabric.  In  both 
plant  and  animal  it  is  however  manifest  that  they  exercise 
the  same  function,  and  are  intimately  connected  with  the 
nutrition  of  the  different  parts  of  the  organism. 

Thus  the  plant  and  the  animal  are  closely  allied  to  each 
other.  Histology  has  demonstrated  not  the  analogy,  but 
the  absolute  identity  of  growth  in  the  animal  and  the 
plant.  Nutrition  and  reproduction  in  animals,  is  as  clearly 
a  vegetative  process,  as  that  the  sun  shines  in  the  heavens. 


COMPARED  WITH  THOSE  OP  ANIMALS.  73 


• 
CHAPTER  IV. 

ON  THE  CONTRACTILITY  OF  THE  TISSUES. 

LIFE  in  the  higher  order  of  animals  consists  in  the 
exercise  of  four  grand  functions,  viz.,  nutrition  and  repro- 
duction, which  they  possess  in  common  with  plants,  and 
which  constitute  their  vital  or  vegetative  functions;  loco- 
motility  and  sensibility  which  are  their  special  and  dis- 
tinctive appendage,  and  which  form  their  animal  functions, 
properly  so  called,  because  it  is  these  which  constitute 
their  special  character  of  animality. 

Now  the  plant  is  a  beautifully  simplified  and  highly  in- 
structive representation  of  the  laws  of  growth  and  repro- 
duction in  the  animal. 

There  is  no  nervo  muscular  apparatus  to  give  motion  to 
the  organism  of  plants.  Their  movements  are  plainly  at- 
tributable, in  the  great  majority  of  cases,  to  agencies  purely 
mechanical.  Their  branches,  leaves,  and  other  organs,  are 
moved  by  the  wind,  not  by  nerves  and  muscles.  Some 
species,  however,  exhibit  movements,  arising  from  other 
causes  as,  for  example,— 

The  Dionoea  muscipula,  or  Venus'  s  Fly-catcher.  This 
remarkable  plant  grows  in  great  abundance  in  the  sandy 
swamps  in  the  neighborhood  of  the  Cape  Fear  River, 
especially  from  Wilmington  to  Fayetteville,  North  Caro- 
lina ;  but  it  has  not  yet  been  found  in  any  other  locality. 

The  generic  name  of  the  plant,  Dionoea,  is  a  derivative 
from  Dione,  one  of  the  names  of  Venus.  The  elegance 
and  delicacy  of  its  snow-white  corolla  are  alluded  to  in  the 
7 


74 


THE  TISSUES  OF  PLANTS 


generic  name.  It  is  called  specifically  muscipula,  or  fly- 
catcher, with  reference  to  its  curious  habit  of  catching  flies 
with  its  leaves,  which  are  organized  expressly  for  this  pur- 
pose. The  leaves  have  a  broad,  dilated  petiole,  and  the 
lamina  or  blade,  which  is  somewhat  circular  in  outline,  is 
connected  by  a  joint  with  its  top.  The  margin  of  the 
lamina  is  fringed  with  a  row  of  stiff  bristles  or  hairs ;  three 
shorter  and  more  slender  ones,  with  swellings  at  their  base, 
are  placed  on  the  upger  surface  of  the  leaf,  in  a  triangular 
position,  on  either  side  of  the  midrib.  It  is  in  these  last 
that  the  irritability  chiefly  resides. 

Fig.  19. 


Fig.  19  represents  a  portion  of  the  stem  and  leaves  of  Venus's  Fly-trap.  The 
leaf  consists  of  two  parts,  a  lamina  or  blade,  I,  and  a  petiole  or  stalk,  p.  The 
two  sides  of  the  lamina  are  united  by  a  sort  of  hinge,  and  on  the  expanded  leaf 
a,  the  three  hairs  may  be  seen  on  each  half  of  the  lamina,  which,  when  touched, 
cause  it  to  fold  up,  as  represented  at  6. 

"When  an  insect,  in  traversing  the  lamina,  touches  these 
sensitive  hairs,  the  two  sides  of  the  lamina  suddenly  come 
into  contact ;  the  bristles  with  which  they  are  fringed 
interlace  like  the  fingers  of  the  hands  when  clasped,  and 


COMPARED  WITH  THOSE  OP  ANIMALS.  75 

the  insect  is  as  effectually  caught  in  this  vegetable  snare 
as  a  rat  in  a  steel  trap.  If  it  should  escape  the  teeth  of 
the  trap,  which  is  seldom  the  case,  its  only  chance  of 
liberty  consists  in  lying  perfectly  still,  when  the  leaf,  freed 
from  all  sources  of  irritation,  would  gradually  unclose ;  this, 
of  course,  the  insect  never  does,  but  continues  struggling 
for  freedom  till  it  is  ultimately  crushed  to  death  by  the 
plant.  Flies  and  other  insects  are  often  found  dead  on  the 
leaves,  which  have  been  killed  in  this  way. 

The  experiments  of  Mr.  Knight  on  the  Dioncea  would 
almost  prove  it  to  be  a  carnivorous  vegetable.  A  detailed 
account  of  them  may  be  read  in  the  article  on  botany, 
"Lardner's  Cabinet  Cyclopaedia."  The  following  is  the 
substance  of  what  is  there  stated.  Mr.  Knight  cultivated 
specimens  of  the  Dioncea  in  separate  pots  in  a  suitable 
soil.  From  the  leaves  of  some  of  them  all  the  bristle  were 
removed,  but  the  plants  were  otherwise  uninjured,  and 
pieces  of  scraped  beef  were  placed  on  their  surfaces.  The 
other  specimens  were  allowed  to  retain  their  bristly  fringe 
and  irritable  hairs  on  their  leaves,  and  had  as  much  light, 
air,  and  water  as  their  disarmed  neighbors ;  but  all  flies 
were  prevented  from  gaining  access  to  them.  The  result 
of  the  experiment  showed  the  more  flourishing  condition  of 
the  provisioned  specimens  I 

The  Hedysarum  gyrans,  or  moving  plant  of  British 
India.  A  portion  of  the  stem  and  leaf  of  this  wonderful 
plant  is  seen  in  our  engraving.  The  leaves  of  this  plant 
are  in  constant  motion  by  night  and  by  day.  We  know 
that  there  may  be  motion  in  animals  without  consciousness, 
as,  for  instance,  during  deep  sleep.  The  functions  of  ani- 
mal life,  which  consist  in  sensation  and  locomotion,  are 
then  totally  suspended,  and  those  of  vegetable  life  are  fa  full 
activity.  Circulation  and  respiration,  by  means  of  which 


76  THE  TISSUES  OF  PLANTS 

nutrition  is  carried  on  in  both  animals  and  plants,  proceeds 
during  the  period  of  repose.  The  heart  continues  its  pul- 
sations, and  the  blood  is  aerated  in  the  lungs.  In  the 
Hedysarum  gyrans,  we  have  a  parallel  instance  of  the  same 
perpetuity  of  motion. 

Fig.  20. 


Compound  leaf  of  Hedysarum  gyrans,  having  two  pairs  of  leaflets,  5,  articu- 
lated to  the  petiole,  and  a  large  terminal  leaflet. 

The  terminal  leaflet  appears  to  be  peculiarly  sensitive  to 
light.  It  takes  the  position  represented  in  the  figure 
during  the  night,  but  becomes  horizontal  during  the  day- 
time, its  midrib  forming,  with  the  petiole,  a  continuous 
and  direct  line.  The  terminal  leaf  is,  however,  manifestly 
depressed  if  the  plant  is  only  placed  in  the  shade  for  a  few 
minutes.  In  the  changes  of  its  position  with  reference  to 
the  ever  varying  intensity  of  light  throughout  the  day,  the 
terminal  leaf  forms,  in  fact,  a  natural  photometer  or  light 
measurer  of  great  delicacy  and  power. 

The  movements  of  the  lateral  leaflets  are,  on  the  con- 
trary, entirely  independent  of  the  influences  of  light,  and 


COMPARED  WITH  THOSE  OF  ANIMALS.  77 

are  continuous  by  night  and  by  day,  even  when  the  ter- 
minal leaflet  is  asleep.  They  move,  like  the  second-hand 
of  a  time  keeper,  by  a  succession  of  little  jerks,  each  leaflet 
describing  the  arc  of  a  circle  with  its  point.  Whilst  one 
leaflet  is  rising,  the  other  is  sinking,  but  in  such  a  manner 
that  the  axes  of  both  leaflets  always  remain  in  the  same 
straight  line.  These  movements,  although  independent  of 
light,  are  rendered  more  active  by  heat,  and  by  a  more 
vigorous  and  healthy  condition  of  the  plant.  The  point  of 
the  leaflets  describe  the  arc  in  about  thirty  or  forty  seconds ; 
the  movement  then  stops  for  about  a  minute,  and  is  again 
resumed  in  the  contrary  direction.  No  satisfactory  ex- 
planation of  these  movements  has  yet  been  given. 

This  plant  belongs  to  the  natural  order  Leguminosce,  of 
which  the  pea  and  bean  are  familiar  examples. 

The  Mimosa  pudica  or  sensitive  plant.  Everybody  has 
heard  about  this  plant,  and  we  should  think  that  many 
of  our  readers  have  seen  it.  Its  movements,  when  touched, 
would  almost  seem  to  imply  in  it  an  obscure  degree  of 
consciousness;  but  if  the  phenomena  be  more  carefully 
examined,  however  closely  they  may  correspond  with  the 
effects  of  sensation  and  instinct,  it  appears  very  certain 
that  they  flow  from  simpler  principles. 

The  leaf  of  the  sensitive  plant  is  a  compound  bipinnate 
one,  having  four  partial  leaf-stalks  proceeding  from  a  com- 
mon petiole.  The  small  pinnules  or  leaflets  are  expanded 
horizontally  when  the  plant  is  in  the  light  and  unmo- 
lested ;  but  when  it  is  in  darkness,  as  well  as  when  the 
leaves  are  touched  or  irritated,  the  pinnules  fold  upwards, 
so  as  to  bring  their  upper  surfaces  into  contact;  and  at 
length  the  impulse  reaches  the  base  of  the  leaf-stalk,  which 
immediately  drops  downward.  When  the  pinnules  are 
thus  folded  together,  and  the  leaf-stalks  depressed,  the 


78  THE  TISSUES  OF  PLANTS 

plant  appears  as  if  it  were  withered  and  dead ;  but  if  it  be 
let  alone,  after  awhile,  the  leaflets  gradually  separate  from 
each  other,  and  also  the  partial  petioles ;  the  main  petiole 
gently  rises  to  its  former  angular  position  with  reference 
to  the  stem,  and  the  plant  resumes  its  usual  appearance. 

Fig.  21. 


Branch  and  leaves  of  the  sensitive  plant  (Mimosa  pvdica),  showing  the 
petiole  in  its  erect  state,  a,  and  in  its  depressed  state,  & ;  also,  the- leaflets  closed, 
c,  and  the  leaflets  expanded,  d. 

If  the  plant  is  sickly,  the  position  of  the  leaves  remains 
permanently  the  same,  and  no  sensible  motion  follows  any 
kind  of  excitement.  When,  however,  it  is  in  a  healthy 
state,  it  is  difficult  to  approach  without  disturbing  it.  Even 
the  shaking  of  the  ground  caused  by  the  tramp  of  a  horse 
will  cause  the  mimosa  to  fold  its  leaves. 

These  movements  are  manifested  both  in  darkness  and 
in  light,  in  water  as  well  as  air.  They  are  also  produced 
by  the  light  of  the  sun  concentrated  by  a  burning-glass, 
or  by  a  drop  of  any  irritating  fluid,  such  as  sulphuric  or 
nitric  acid. 


COMPARED  WITH  THOSE  OP  ANIMALS.  79 

The  seat  of  motion  in  the  sensitive  plant,  is  evidently  in 
the  little  swelling  or  intumescence  at  the  articulation  of 
the  general  and  partial  leaf-stalks.  These  swellings,  when 
touched  directly,  communicate  motion  to  the  leaves.  They 
appear  to  have  two  surfaces,  possessing  different  degrees  of 
irritability.  When  these  swellings  are  gently  touched  with 
a  steel  point  on  their  upper  surface,  the  leaflets  immediately 
fold  together ;  but  they  do  not  move  when  the  lower  sur- 
face of  the  swellings  is  touched.  With  the  swellings  at 
the  base  of  the  main  petiole,  it  is  just  the  reverse ;  for  the 
irritability  resides  not  in  their  upper,  but  in  their  lower 
surface. 

Up  to  the  present  moment,  no  satisfactory  explanation 
of  these  movements  has  been  afforded.  The  opinion  most 
favorably  received  amongst  scientific  men  with  respect  to 
them  is,  that  they  are  referable  to  a  power  of  contractility 
possessed  by  the  tissues  of  the  plant,  analogous  to  that 
which  exists  in  certain  animal  tissues,  but  especially  in 
the  muscular.  It  is  well  known  to  naturalists  that  certain 
unicellular  and  thread-like  plants,  found  amongst  the  green 
hair-like  vegetation  which  attaches  itself  to  stones  in  fresh 
water  rivulets,  possess  this  power  of  contractility  under  the 
influence  of  external  stimuli.  If  this  capillary  vegetation 
be  placed  beneath  the  microscope,  movements  among  some 
of  the  filaments  will  be  distinctly  recognized.  These  plants 
have  been  called  oscillatorias,  in  allusion  to  these  motions, 
which  resemble  vibrations  or  oscillations  to  and  fro,  and 
occasionally  writhing  movements  so  well  marked,  that  their 
vegetable  nature  has  been  disputed.  This  property  of  con- 
tractility exhibited  by  these  isolated  filaments,  is  manifested 
by  them  when  associated  together,  in  the  case  of  the  mi- 
mosa. The  movements  of  the  mimosa  or  sensitive  plant, 
are  probably  produced  by  this  cause,  and  are  closely  allied 


80  THE  TISSUES  OF  PLANTS 

to  the  motions  visible  in  the  lowest  and  simplest  animal, 
which  are  equally  destitute  of  a  nervous  and  muscular 
system. 

The  sensitive  plant  of  the  conservatories  does  not  greatly 
exceed  in  irritability  the  shrankia,  or  wild  sensitive  plant 
of  the  Southern  States,  the  leaves  of  which  promptly  close 
when  touched  by  the  hand  or  the  foot  of  the  traveller. 
Indeed,  there  is  more  than  one  sensitive  plant  in  the 
world ;  the  vegetable  -creation  teems  with  these  faint  fore- 
shadowings,  as  it  were,  of  those  higher  powers  of  life 
manifested  by  animals. 

To  the  same  cause,  that  is  to  say,  vegetable  irritability, 
or  the  contractility  of  the  tissues,  is  to  be  attributed,  the 
curvature  of  the  tendrils  or  even  of  the  stems  of  weak 
plants  around  the  objects  to  which  they  become  attached. 
In  cases  where  tendrils  only  are  put  forth,  the  irritability 
appears  to  be  confined  to  them ;  but  when  the  whole  stem 
acts  as  a  tendril,  it  seems  to  be  diffused  through  its  entire 
length. 

That  the  irritability  of  the  tendrils  produces  the  spiral 
attachment  of  themselves  to  the  bodies  with  which  they 
are  brought  into  immediate  contact,  is  capable  of  direct 
experimental  proof.  All  tendrils  are  first  put  forth  in  a 
right  line,  which  is  curved  into  a  sort  of  hook  at  its  apex. 
If,  whilst  the  tendril  is  in  the  condition,  a  twig  or  young 
shoot  be  rubbed  against  it  a  little  below  the  hook,  in  a  few 
minutes,  the  tendril  will  be  seen  to  be  curving  round  the 
twig,  and  if  the  friction  be  continued,  the  regular  spiral 
attachment  will  be  ultimately  formed.  These  phenomena 
must  therefore  be  classed  with  the  movements  of  the 
mimosa,  as  they  are  probably  only  feebler  manifestations 
of  the  same  principle. 

All  the  movements  executed  by  vegetables  are  only  par- 


COMPARED  WITH  THOSE  OP  ANIMALS.  81 

tial  in  their  character.  None  of  them  enjoy  the  faculty  of 
displacing  themselves  in  toto  and  removing  to  another  spot 
more  favorable  to  their  growth.  When  unfavorably  located, 
seeds  either  perish,  or  the  germination  and  subsequent 
growth  of  the  plant  is  greatly  retarded.  In  a  word,  volun- 
tary locomotion  exists  only  in  animals. 

That  the  nutritive  functions  of  animals  are  affected  by 
nervous  influences,  many  facts  abundantly  prove.  In  blush- 
ing, the  nerves  evidently  affect  the  blood,  which  is  the  grand 
vehicle  of  nutritive  matter  in  animals,  enlarging  the  capil- 
laries and  bringing  it  in  an  increased  flow  to  the  surface;  a 
person  affrighted  becomes  pale,  the  nerves  contracting  the 
capillaries  and  driving  the  blood  from  the  countenance. 
Bad  news  will  affect  the  appetite,  and  prevent  the  healthy 
action  of  the  digestive  organs.  The  sight  of  food  will  pro- 
duce a  flow  of  the  secretion  from  the  salivary  glands  of  the 
mouth,  necessary  for  its  lubrication ;  and  the  excitement 
created  in  the  mother  by  the  mere  presence  of  the  new-born 
infant,  will  bring  a  draught  of  milk  into  the  breast.  Grief 
will  render  the  eye  tearful,  or  even  tearless.  There  are  no 
such  nervous  influences  to  interfere  with  the  nutritive  pro- 
cesses in  plants. 

Even  the  reproductive  functions,  which  in  animals  are  far 
more  intimately  associated  with  the  nerves  than  those  of 
nutrition,  in  plants,  generally  speaking,  are  unmarked  by 
any  higher  vital  phenomena  than  that  which  is  manifested 
in  the  evolution  of  the  other  parts  of  the  organism.  The 
fecundation  of  the  germ  is  effected  by  an  appropriate 
arrangement  of  the  organs,  and  the  embryo  is  freed  from 
the  ovary  by  a  mechanical  rupture  of  the  parts,  or  by  other 
physical  means.  The  whole  process  is  simply  vegetative. 

In  some  few  species,  however,  such  as  the  barberry 
(Berberis  vulgaris,)  and  mountain  laurel,  (Kalmialatifolia,) 


82  THE  TISSUES  OF  PLANTS. 

the  stamens  exhibit  active  movements  during  the  period  of 
fecundation,  and  these  movements  are  evidently  made  in 
order  to  secure  the  proper  application  of  the  pollen  to  the 
stigma  of  the  pistil.  These  parts  are  probably  subject  to  a 
similar  principle  of  contractility  to  that  which  influences 
the  movements  of  the  leaves  of  the  mimosa. 

The  organization  of  plants  corresponds  with  this  simpli- 
city of  their  functions.  We  have  already  indicated  the 
predominance  in  animals  of  nitrogen,  which  exists  only 
sparingly  in  plants.  Analysis  also  only  shows  us  two  ele- 
mentary tissues  in  plants,  the  cellular  and  the  vascular, 
whereas  we  find  in  animals  six,  viz :  the  cellular,  the 
fibrous,  the  muscular,  the  nervous,  the  osseous,  and  the 
cartilaginous;  the  last  four  being  developed  especially  in 
connection  with  their  superadded  functions  of  sensation  and 
locomotion. 

We  have  therefore  in  the  plant,  the  functions  of  nutri- 
tion and  reproduction,  operating  under  greatly  simplified 
conditions.  It  is  therefore  proper  to  begin  with  the  plant 
as  introductory  to  the  study  of  the  more  complicated  con- 
ditions under  which  vegetative  life  exists  in  the  animal. 


PART  II. 


NUTRITION  IN  PLANTS  AND  ANIMALS. 


CHAPTER  V. 

ON     THE    ABSORPTION    AND    CIRCULATION    OP    FOOD     IN 
PLANTS  AND  ANIMALS. 

The  vegetative  functions  of  nutrition  and  reproduction, 
have  for  their  principal  object  the  support  of  life  in  the 
different  individuals,  and  the  multiplication  and  propaga- 
tion of  their  species. 

Nutrition  is  undoubtedly  the  most  important  and  general 
of  the  functions  of  animal  and  vegetable  life.  It  operates 
in  a  continuous  manner,  commencing  with  life  and  ceasing 
only  at  its  termination,  whilst  the  other  functions  manifest 
themselves  only  under  certain  conditions,  and  at  determinate 
epochs. 

Nutrition  in  plants  and  animals  is  a  very  complicated 
function,  and  implies  several  distinct  acts  :  1.  The  intro- 
duction of  food  into  the  interior  of  the  organism,  (absorp- 
tion.) 2.  Its  distribution  to  all  its  parts,  (circulation.) 
3.  The  elaboration  of  the  nutritive  fluid  by  contact  with 
the  air,  (respiration.)  4.  Its  conversion  into  the  substance 
of  the  organism,  (assimilation.)  5.  The  elimination  of  such 
matters  as  are  not  necessary,  (excretion.) 

ABSORPTION  IN  PLANTS  AND  ANIMALS. 

Before  food  can   enter  the  tissues  of  any  organized 
being,  whether  animal  or  plant,  it  must  be  reduced  to  a 
8 


86  THE  NUTRITIVE  FUNCTIONS. 

fluid  or  gaseous  condition.  This  is  absolutely  necessary,  in 
order  to  render  it  susceptible  of  being  conveyed  through 
the  vessels  and  of  permeating  the  walls  of  the  cells,  which 
we  have  seen  to  be  the  ultimate  structure  of  the  organism 
of  both  plants  and  animals.  With  reference  to  plants,  no 
such  reduction  of  their  food  to  a  gaseous  or  fluid  state  is 
necessary,  because  they  live  in  the  midst  of  their  food,  and 
in  perpetual  contact  with  it. 

If  we  plant  a  seed  in  the  ground,  it  grows  from  the  very 
commencement  of  vital  motion,  in  two  opposite  directions, 
upwards  into  the  atmosphere  and  downwards  into  the 
earth :  the  two  grand  sources  from  whence  it  obtains  the 
materials  which  contribute  to  its  future  growth.  We  may 
consider  a  plant  then  as  a  vegetable  axis  or  stem,  more  or 
less  ramified  at  its  two  extremities.  That  portion  of  the 
stem  growing  into  the  atmosphere  puts  forth  from  its 
branches,  during  the  season  of  vegetable  activity,  certain 
flat,  dilated  organs,  which  we  call  leaves,  the  surface  of 
which  is  porous  and  by  means  of  which  food  is  absorbed 
from  the  atmosphere.  That  portion  of  the  stem  which 
ramifies  in  the  ground,  on  the  other  hand,  becomes  covered, 
about  the  same  time,  with  numberless  delicate  white  fibres, 
which  are  the  true  roots  of  the  plant.  These  correspond 
to  the  leaves  on  the  branches,  performing  the  same  func- 
tion, that  of  absorption,  and  like  the  leaves  decay  and 
become  detached  from  the  plant  in  autumn.  On  the 
return  of  spring,  the  underground  and  atmospheric  rami- 
fications of  the  plant  are  again  re-clothed,  the  former  with 
fibres  and  the  latter  with  leaves. 

It  is  a  mistake  to  suppose  that  all  the  underground  por- 
tion of  a  plant  is  the  root.  The  white  delicate  fibres  put 
forth  in  early  spring,  at  the  time  that  the  leaves  .grow  on 
the  branches  in  the  atmosphere',  are  the  true  roots ;  they 


ABSORPTION.  87 

contribute  to  the  extension  of  the  subterranean  branches 
by  the  food  which  they  absorb  from  the  soil,  exactly  as  the 
leaves  induce  a  growth  of  the  branches  in  the  atmosphere 
by  exercising  the  same  function.  A  fibre  and  a  leaf  are 
wonderfully  different  in  form  and  color,  yet  both  are  ab- 
sorbents, beautifully  adapted  to  the  media  in  which  they 
develop. 

The  plant  is  nourished  by  inorganic  substances,  Oxygen, 
Hydrogen,  Carbon,  Nitrogen,  and  some  mineral  salts. 
Analysis  shows  us  these  elementary  substances  in  plants, 
which  combining  among  themselves,  form  all  their  various 
and  diversified  products.  These  elementary  substances 
exist  only  in  the  earth  and  atmosphere,  the  two  grand 
sources  of  all  vegetable  nutrition.  Sometimes  they  exist 
there  fcin  an  isolated  state,  or  they  make  part  of  other 
combinations,  which  the  plant  has  the  power  to  destroy 
in  order  to  appropriate  them  to  itself. 

Water  is  necessarily  the  vehicle  of  the  alimentary  sub- 
stances of  plants.  It  enters  the  plant  from  the  .earth,  ac- 
cording to  the  common  laws  of  endosmosis  and  capillarity, 
by  the  delicate  hair-like  fibres  of  the  roots.  The  leaves 
favor  this  absorption  by  the  evaporation  which  is  continu- 
ally taking  place  from  their  surface,  which  renders  addi- 
tionally thick  and  mucilaginous  the  fluid  in  the  leaf-cells, 
and  throughout  the  organism  of  the  plant.  The  leaves 
also  absorb  water  from  the  atmosphere,  which  always  exists 
there  more  or  less  in  a  state  of  vapor,  but  principally  car- 
bonic acid,  which  enters  largely  into  the  composition  of  the 
vegetable  framework. 

So  long  as  the  roots  can  absorb  as  much  water  as  the 
leaves  evaporate,  the  plant  will  appear  fresh  and  green,  but 
-the  foliage  droops  (as  is  often  seen  on  a  hot  summer's  day 
towards  noon,)  when  the  evaporation  from  the  leaves  ex- 


88  ^    THE  NUTRITIVE  FUNCTIONS. 

eeeds  the  supply  at  the  roots.  A  copious  supply  of  water, 
however,  usually  accumulates  on  the  leaves  during  the 
cloudless  nights  of  summer,  which  is  absorbed  through  the 
pores  on  their  surface  into  their  organism,  and  in  the  mor- 
ning, the  plants  refreshed  by  the  night  dews,  have  assumed 
their  wonted  rigidity  and  freshness.  In  this  case  the  only 
absorbents  are  the  stomata  on  the  epidermis.  How  beauti- 
ful this  provision  of  nature,  which,  at  the  time  the  soil  is 
dried  to  dust,  causes  the  moisture  to  distil  from  the  atmos- 
phere on  every  forest  leaf  and  blade  of  grass  in  gently 
descending  dews,  to  remedy  as  it  were  in  some  measure  the 
evils  arising  from  an  insufficiency  .of  water  in  the  soil. 

The  stomata  or  pores  of  plants  vary  in  their  figure  and 
size.  They  are,  however,'  usually  of  an  oval  shape  with  a 
slit  in  the  middle,  and  are  so  situated  as  to  open  directly 
into  the  intercellular  spaces  of  the  parenchyma.  These 
pores  may  be  called  the  vegetable  governor.  They  regulate 
and  control  the  evaporation  from  the  surface  of  plants,  thus 
promoting  a  healthy  passage  of  the  fluids  through  the 
system. 

This  is  done  on  the  following  principle.  The  slit  or  per- 
foration in  the  epidermal  surface  lies  between  two  cells, 
which  differ  from  the  other  in  being  very  hygometrical,  or 
easily  affected  by  the  moisture  of  the  atmosphere.  When 
the  air  is  damp,  and  there  is  an  abundance  of  moisture  in 
the  ground,  these  two  cells  become  swollen  and  turgid,  and 
by  their  outward  curvature  open  the  pore  and  allow  the 
escape  of  the  superfluous  water ;  but  when  the  atmosphere 
is  dry  they  straighten  and  lie  parallel,  their  sides  being 
brought  into  close  contact.  The  pore  is  thus  closed,  and 
the  evaporation  stopped  the  moment  it  becomes  injurious 
to  the  plant. 

The  structure  of  the  stomata  or  pores  of  plants  may  be 


ABSORPTION. 


readily  perceived  on  the  epidermis  of  the  lily,  where  they 
are  unusually  large.  The  epidermis  must  be  first  carefully 
removed  from  one  of  the  leaves,  and  having  been  freed 
from  all  its  chlorophyl,  or  green  matter,  it  must  be  placed 

Fig.  22. 


Epidermis  of  the  white  lily,  showing  the  stomata  st,  composed  of  two  c«ll«, 
with  an  opening  or  slit  between  them. 

between  two  slips  of  glass,'  with  a  drop  of  water  between 
them,  so  as  to  give  it  the  necessary  degree  of  transparency. 
Water  ought  always  for  this  reason  to  be  used,  whenever 
objects  selected  from  the  tissues  of  plants  are  examined 
microscopically.  The  epidermis,  thus  prepared,  will  ex- 
hibit these  pores,  and  the  nature  and  beauty  of  their 
mechanism  will  be  seen  and  appreciated. 

It  must  be  evident  to  all  practical  men,  from  these  facts, 
that  it  is  of  some  importance  to  keep  the  leaves  of  plants 
free  from  all  impurities,  which  are  apt  to  accumulate  on 
their  surface  and  thus  choke  up  their  porous  openings. 
During  dry  seasons,  a  supply  of  water  to  the  leaves  is  of  as 

8* 


90  THE  NUTRITIVE  FUNCTIONS, 

much  importance  as  a  moistened  soil.  House-plants  fre- 
quently suffer  from  the  dust  with  which  their  leaves  become 
covered.  Their  health  and  general  appearance  may  be 
very  much  improved,  by  a  careful  cleansing  of  their  leaves 
every  other  day,  with  a  wet  sponge.  It  is  as  important  to 
keep  the  epidermis  of  a  plant  in  a  cleanly  state  as  the  skin 
of  an  animal.  Neglect  in  either  instance  brings  on  disease, 
premature  decay,  and  loss  of  vitality. 

The  food  of  animals  is  not  furnished  to  them  in  a 
condition  fit  for  assimilation  and  circulation.  It  comes  into 
contact  with  their  organs  in  a  more  or  less  solid  state,  and 
a  cavity  is  therefore  provided  in  the  interior  of  their 
organism  for  its  reception,  and  reduction  to  a  condition  fit 
to  enter  the  circulation. 

We  have  seen  that  one  of  the  most  striking  differences 
between  animals  and  plants  is  the  possession  by  the  former 
of  a  nervous  system  of  which  the  latter  are  totally  deprived. 
This  nervous  system  is  the  seat  of  all  the  sensations  and 
movements  of  animal  life.  It  manifests  itself  in  the  un- 
erring instincts  of  inferior  creatures,  enabling  them  to  pro- 
cure themselves  food  and  defend  themselves  against  their 
enemies,  and  in  those  higher  attributes  of  reason  and  reflec- 
tion which  appear  gradually  in  the  lower  animals,  and 
obtain  in  man,  "  the  minister  and  interpreter  of  nature," 
their  noblest  and  most  exalted  expression.  Creatures  thus 
endowed  must  provide  food  for  themselves.  It  domes  to 
them  no  more  mechanically  and  chemically. 

Thus,  at  the  very  outset,  the  nutritive  apparatus  of 
animals  is  much  more  complicated  than  that  of  plants. 
Their  food  has  to  be  both  procured  and  prepared  by  them- 
selves, before  it  can  be  assimilated.  They  are  provided 
with  senses  and  appropriate  organs  for  this  very  purpose, 
and  they  must  exercise  both  if  they  would  obtain  the 


ABSORPTION.  91 

necessary  aliment.  These  senses  and  organs  appear  to  be 
gradually  superadded  to  the  simple  digestive  cavity  which 
constitutes  the  entire  organism  of  the  lowest  animal.  The 
organic  apparatus  for  the  prehension  and  preparation  of  the 
food  prior  to  its  introduction  into  the  interior  of  the  diges- 
tive cavity,  becomes  more  complicated  as  we  ascend  in  the 
scale  of  organization. 

The  organs  of  prehension  and  preparation  are  most  ad- 
mirably adapted  to  the  peculiar  food,  habits,  and  instincts 
of  each  animal.  In  man,  whose  wants  are  infinitely  more 
numerous,  these  organs  exist  in  the  highest  condition  of 
development.  He  is  provided  with  a  hand,  which  may  be 
justly  regarded  as  the  most  perfect  of  prehensible  instru- 
ments. To  the  skillful  use  of  this  organ,  under  the  guid- 
ance of  reason,  he  owes  his  superiority  over  the  other 
animals,  whose  anterior  members  are  organized  more  for 

Fig.  23. 


the  support  of  their  bodies  than  for  the  seizure  of  objects. 
The  other  organs  consist  of  an  alimentary  tube  or  canal 


92  THE  NUTRITIVE  FUNCTIONS. 

more  or  less  dilated  in  its  course  through,  the  body.  At 
the  upper  portion  of  this  canal  there  is  an  opening  called 
the  mouth,  which  is  provided  with  an  appropriate  arrange- 
ment of  teeth  for  cutting  and  crushing  the  food,  and  of 
salivary  glands  for  affecting  its  lubrication. 

The  food  having  been  prepared  and  lubricated  in  this 
manner^  descends  into  the  stomach  through  the  oesophagus 
(1,)  by  the  left  or  cardiac  opening  where  it  is  acted 
on  by  the  gastric  juice  secreted  by  the  walls  of  the  sto- 
mach (3.)  This  fluid,  which  is  of  an  acid  nature,  re-acts 
on  the  alimentary  mass,  penetrates,  softens,  and  ultimately 
changes  it  into  a  semi-fluid,  homogeneous,  and  pulpy  sub- 
stance, named  chyme.  At  the  commencement  of  this  ope- 
ration, the  communication  between  the  stomach  and  intes- 
tines is  entirely  closed  by  a  valve,  called  the  pylorus  (5.) 
As  the  solution  advances,  the  dissolved  parts  are  gradually 
moved  by  the  muscular  contractions  of  the  walls  of  the 
stomach  to  its  right  or  pyloric  extremity  (4.)  The  valve 
called  the  pylorus  is  a  very  faithful  sentinel.  This  is  indi- 
cated by  its  name,  which  is  derived  from  two  Greek  words, 
and  signifies  literally,  to  guard  the  gate.  It  will  not  ordi- 
narily permit  any  undigested  food  to  pass  it.  The  quan- 
tity of  chyme,  or  digested  food,  which  passes  through  the 
^pylorus,  is  at  first  small,  but  as  the  process  of  chymifica- 
tion  or  digestion  goes  on,  the  flow  increases,  and  towards 
its  termination,  the  chyme  passes  quite  rapidly  through 
the  valve.  In  the  duodenum,  which  commences  the  small 
intestine,  the  chyme  is  acted  upon  by  the  fluids  secreted  by 
the  liver  and  pancreas,  that  is  to  say,  by  the  bile  and  pan- 
creatic fluids,  which  are  poured  into  the  upper  part  of 
the  small  intestines  by  means  of  a  duct  (6,)  communica- 
ting with  these  organs.  These  fluids,  which  are  of  an  alka- 
line nature,  probably  arrest  the  movement  -  of  dissolution 


ABSORPTION.  93 

produced  by  the  gastric  juice.  In  consequence  of  this 
new  action  upon  the  chyme,  in  passing  through  the  small 
intestine,  it  is  separated  into  a  fluid  of  a  whitish  color  named 
chyle,  which  as  soon  as  it  is  formed,  is  absorbed  by  the 
radicles  of  a  special  system  of  vessels  named  chiliferous 
vessels  or  lacteals;  these  reunite  into  branches  more  or 
less  voluminous,  and  ultimately  meet  in  a  common  trunk 
called  the  thoracic  duct.  This  duct,  which  is  about  the 
size  of  a  common  quill,  conveys  the  chyle  to  its  point  of 
junction  with  the  sub-clavian  vein  at  the  lower  part  of  the 
neck,  pouring  it  into  the  torrent  of  the  circulation.  Res- 
piration gives  to  the  fluid  thus  mingled  with  the  blood  its 
finishing  change,  so  that  the  two  become  identical.  The 
blood  thus  enriched,  is  spread  through  every  part  of  the 
body  both  external  and  internal,  by  means  of  the  capil- 
laries interjacent  between  the  arterial  and  venous  ramifica- 
tions, thus  furnishing  to  the  system  the  necessary  supply 
of  nutrient  matter. 

The  absorption  of  food  into  the  organism  is,  therefore, 
in  principle,  precisely  the  same  in  animals  as  in  plants,  with 
this  difference,  that  there  is  superadded  to  the  organism 
a  highly  complicated  nervo-muscular  apparatus  for  its  pre- 
hension and  preparation.  The  introduction  of  food  into  the 
digestive  cavity  or  stomach,  is  wholly  a  voluntary  act,  and 
results  from  the  exercise  of  the  functions  of  animal  life ; 
its  digestion  and  absorption  when  there,  is  altogether  in- 
voluntary. The  whole  process  of  chymification  and  lacteal 
absorption  proceeds  without  our  consciousness,  and  cannot 
be  controlled  by  any  effort  of  our  will.  All  these  internal 
motions  are  therefore  purely  vegetative  acts,  proceeding 
from  the  operation  of  that  life  which  we  possess  in  common 
with  plants. 

This  truth  will  be  more  apparent  if  the  reader  will  only 


94  THE  NUTRITIVE  FUNCTIONS- 

reflect  for  one  moment.  The  food  in  the  stomach  and  in- 
testines is  as  much  external  to  the  living  body  as  it  was 
before  its  introduction  into  those  cavities,  until  it  is  taken 
up  by  the  absorbents  which  line  their  walls ;  and  it  is  re- 
moved from  those  cavities  by  the  radicals  of  the  chyliferous 
vessels  and  afterwards  diffused  to  all  parts  of  the  animal, 
just  as  the  roots  of  plants  absorb  food  from  the  soil,  which 
is  afterwards  conveyed  by  the  trunk  to  the  branches  and 
highest  extremities.  "  Whilst,  therefore,  the  roots  of 
plants,  ramify  througn  the  soil  in  quest  of  food,  fixing  the 
plant  to  its  surface,  animals  which  wander  about  from  place 
to  place  in  search  of  the  food  which  they  require,  may  be 
truly  said  to  carry  their  soil  about  with  them."*- 

THE  CIRCULATION  IN  PLANTS  AND  ANIMALS. 

In  the  lowest  forms  of  animals  and  vegetables  where 
the  structure  is  wholly  cellular,  the  movements  of  the  nu- 
tritive fluid  equally  pervade  all  parts  of  the  organism,  pro- 
ceeding forward  and  laterally  from  cell  to  cell  without  fol- 
lowing any  particular  course.  Such  is  also  the  condition 
of  the  circulation  in  the  higher  animals  and  plants  during 
the  embryonic  stage  of  development;  this,  however,  is 
with  them  only  a  transient  condition  of  things.  As  growth 
progresses  in  the  seed  or  ovum,  the  cells  begin  to  manifest 
their  individual  peculiarities,  and  the  young  plant  or  ani- 
mal finally  ruptures  the  envelopes  more  or  less  resisting, 
which  cover  it,  and  speedily  develops  those  organs  neces- 
sary to  its  life  and  increase.  As  specific  processes  are  car- 
ried on  in  distant  parts  of  the  organism,  it  is  necessary 
that  the  nutritive  juice  should  be  conveyed  in  the  proper 
channels,  which  develop  accordingly  for  this  purpose.  In 

*  Carpenter. 


CIRCULATION.  95 

animals  this  movement  is  called  the  circulation  of  the  blood, 
in  plants  the  circulation  of  the  sap ;  in  both,  however,  na- 
ture has  the  same  object  in  view,  the  conveyance  into  all 
parts  of  the  organism,  of  the  elements  which  serve  to  their 
increase  and  nutrition. 

In  the  higher  order  of  animals  the  circulation  is  double, 
that  is  to  say,  the  blood  which  has  deposited  in  every  part 
of  the  body  the  materials  of  nutrition,  returns  to  its  point 
of  departure,  or  to  the  heart,  by  a  series  of  vessels  named 
veins,  from  whence  it  is  driven  by  the  muscular  contrac- 
tions of  the  heart  into  the  lungs,  where,  by  contact  with 
the  atmosphere  it  acquires  new  properties  and  qualities, 
and  returns  a  second  time  to  the  point  from  whence  it  set 
out.  There  is,  therefore,  two  circulatory  circles,  and  at 
the  base  of  each  an  agent  for  impelling  the  blood  into  each 
of  them.  This  agent  consists  in  a  double  cavity  with 
muscular  walls ;  one  of  these  cavities  is  named  the  auricle, 
and  the  other  the  ventricle ;  both  of  them  united  consti- 
tute the  heart,  or  organ  of  impulsion. 

The  auricle  and  ventricle  of  the  right  side  of  the  heart, 
contain  the  dark  venous  blood,  which  returns  impoverished 
from  all  parts  of  the  body ;  the  auricle  and  ventricle  of  the 
left  side  contain  the  bright  red  arterial  blood,  which  arrives 
enriched  from  the  respiratory  organs. 

In  the  mammifera,  with  the  exception  of  the  Dugong, 
-and  in  birds,  there  is  no  direct  communication  between  the 
right  and  left  cavities  of  the  heart,  and  consequently  no 
mixture  of  the  arterial  with  the  venous  blood.  Respiration 
is  therefore  complete,  that  is  to  say,  the  whole  of  the  blood 
which  returns  from  the  different  parts  of  the  body  passes 
into  the  lungs,  and  is  aerated  before  it  is  poured  again  into 
the  torrent  of  the  circulation.  These  animals  are  there- 
fore capable  of  preserving  a  proper  temperature,  indepen- 


96  THE  NUTRITIVE  FUNCTIONS. 

dent  of  that  of  the  medium  in  which  they  live,  and  are 
called  warm-blooded  animals.  But  in  reptiles  and  in 
fishes  the  venous  and  arterial  blood  become  mixed  together, 
the  former  being  only  partially  returned  to  the  lungs; 
hence  respiration  in  these  creatures  is  imperfect,  and  the 
blood  is  cold,  or  rather  in  place  of  having  a  fixed  and  inde- 
pendent temperature,  it  tends  without  ceasing  to  an  equi- 
librium with  that  of  the  surrounding  medium. 

It  follows  from  this,  that,  in  certain  circumstances,  the 
temperature  of  animals  with  cold  blood  is  considerably  ele- 
vated ;  it  is  therefore  better  to  call  the  mammalia,  birds, 
reptiles,  and  fishes,  animals  of  a  fixed  and  variable  tempera- 
ture with  reference  to  the  heat  of  their  blood,  instead  of 
warm  and  cold-blooded  animals.* 

The  course  of  the  blood  in  man  and  the  animals  most 
nearly  allied  to  him  in  organization,  appears  to  be  as  fol- 
lows :  The  blood,  charged  with  the  restorative  materials  of 
nutrition,  is  brought  to  each  organ  by  the  arteries  and  their 
numerous  ramifications.  It  spreads  itself  in  the  tissues  of 
these  organs  by  a  system  of  fine  anastomosing  vessels  called 
capillary  vessels.  In  these  same  organs  arises  another 
order  of  vessels  commencing  where  the  arteries  terminate ; 
these  tubes,  at  first  capillary,  communicate  with  the  arteries, 
and  constitute  by  their  re-union,  the  veins  which  carry  back 
the  blood  which  has  served  to  -nourish  each  organ  to  the 
heart.  The  blood  therefore  flows  in  the  veins  in  a  con- 
trary direction  to  the  current  which  circulates  in  the  arte- 
ries. These  veins  gradually  unite  among  themselves,  and 
finally  form  two  large  trunks  called  the  inferior  and  supe- 
rior vena  cavce.  These  two  vena  cavce  meet  in  the  cavity 
of  the  right  auricle,  from  whence  the  blood  passes  into  a 

*  See  "  Elements  d'Histoire  Naturelle  Medicale,"  par  Achille  Rich- 
ard. Tome  premier.  Premiere  partie.  Zoologie,  page  27. 


CIRCULATION.  97 

Second  cavity  with  thick  and  fleshy  walls  named  the  right 
ventricle.  The  right  ventricle,  in  contracting  powerfully 
upon  itself,  drives  the  blood  through  the  pulmonary  artery 
and  its  innumerable  ramifications  into  the  lungs.  There 
the  blood  is  brought  into  immediate  contact  with  the  air 
absorbed  during  respiration,  and  is  oxygenated  anew,  losing 
a  part  of  its  carbon,  which  forms  the  carbonic  acid  which 
we  expire.  It  is  returned  afterwards  from  the  lungs  by 
the  pulmonary  veins  to  the  left  auricle,  and  from  thence  it 
is  poured  into  the  left  ventricle,  which,  by  its  contractions, 
drives  the  blood  through  the  large  artery  named  the  aorta, 
whose  ramifications  again  carry  it  to  all  parts  of  the  body. 
The  nutrient  fluid  which  circulates  through  the  organic 
tissues  of  plants,  and  which  is  called  sap,  exercises  the 
same  function  in  the  vegetable  that  the  blood  does  in  the 
animal  economy.  Plants,  however,  possess  no  proper 
vessels  within  which -a  true  circulation  is  maintained  by 
the  muscular  action  of  a  central  propelling  organ  or  heart, 
and  the  sap  of  plants  is  not  confined  like  the  blood  of  ani- 
mals to  one  set  of  vessels,  for  owing  to  the  way  in  which 
the  vascular  and  cellular  tissues  of  plants  are  interwoven 
with  each  other,  and  the  general  permeability  of  all  the 
organs,  a  general  transfusion  of  the  sap  takes  place  from 
cell  to  cell,  endosmotically,  and  in  every  direction,  so  that 
the  process  is  in  some  respects  one  of  distribution  as  well 
as  of  circulation.  This  is  particularly  the  case  in  the  em- 
bryos of  flowering  plants  during  the  early  stages  of  their 
growth,  whilst  their  structure  continues  wholly  cellular, 
and  in  those  cryptogamous  plants  which  permanently  re- 
main in  this  low  condition  of  development.  But  as  soon 
as  the  vital  action  of  the  embryo  of  flowering  plants  com- 
mences, and  woody  fibre  and  vascular  tissue  begin  to 
appear  in  its  expanding  organs,  another  force  comes  into 
9 


98  THE  NUTRITIVE  FUNCTIONS. 

play,  that  of  capillary  attraction.  This  last  force  together 
with  that  of  endosmosis,  sufficiently  explains  all  the  pheno- 
mena connected  with  the  motion  of  the  sap  in  plants. 

It  is  well  known  that  if  two  fluids  of  different  densities 
be  separated  from  each  other  by  an  animal  or  vegetable  mem- 
brane, a  mutual  action  will  commence,  the  tendency  of 
which  is  to  produce  an  equilibrium  of  density  between  the 
fluids ;  and  that  the  denser  fluid  will  draw  the  lighter 
through  the  membrane  with  a  force  proportional  to  the 
difference  of  density  of  the  two  fluids.  It  is  also  known 
that  if  a  number  of  delicate  tubes  of  different  sizes  be 
immersed  in  water,  the  water  will  rise  within  the  tubes 
above  its  natural  level  on  the  outside  of  them,  in  propor- 
tion to  the  fineness  of  their  calibre  or  bore. 

Now  in  winter  vegetable  life  is  passive.  The  huge 
oak  tree,  equally  with  the  acorn  that  it  has  cast  upon  the 
earth,  is  torpid  and  inactive,  and  can  no  more  put  forth 
branches  than  the  acorn  can  germinate.  By  the  fall  of  the 
leaves  the  evaporating  orifices  have  been  removed.  The 
cicatrices  or  leaf  scars  are  all  healed,  and  every  pore  is 
carefully  closed  and  sealed  up  against  the  severity  of  the 
weather,  sometimes  by  secretions  especially  elaborated  for 
this  purpose.  The  fluids  in  the  interior  of  the  plant  are  at 
this  time  in  a  state  of  equilibrium.  Capillarity  cannot 
act.  Fluids  do  not  rise  in  capillary  tubes  closed  at  the 
top. 

With  the  return  of  heat  and  light  to  the  earth  in  spring, 
the  fountains  of  nutrition  are  again  unsealed.  The  resinous 
exudation  on  the  buds  is  melted,  the  pores  are  opened,  and 
the  store  of  starch,  oil,  and  other  secretions,  which  always 
exists  in  the  neighborhood  of  all  growing  points,  is  changed 
into  dextrine  and  sugar,  in  consequence  of  the  absorption 
of  the  oxygen  of  the  atmosphere.  The  cells  immediately 


CIRCULATION.  99 

surrounding  the  buds  thus  become  filled  with  a  sap  more 
dense  and  mucilaginous  than  that  contained  in  the  other 
parts  of  the  plant.  The  equilibrium  of  the  fluids  is  thus 
disturbed,  and  a  strong  endosmotic  and  capillary  ascent  of 
the  thin  watery  juices  towards  the  buds  is  gradually 
induced  throughdut  the  entire  organism  of  the  plant,  tend- 
ing to  its  restoration.  At  length  when  the  buds  are 
developed  into  branches,  and  the  young  leaves  are  spread 
abroad  in  the  atmosphere,  the  ascent  of  the  sap  becomes 
powerfully  accelerated  by  the  evaporation  which  takes 
place  at  their  surface. 

Notwithstanding  that  the  sap  is  spread  by  endosmosis 
in  all  directions  through  the  cells  of  plants,  yet  it  is  evi- 
dent that  the  current  will  be  the  strongest  where  capillary 
influences  most  abound ;  consequently,  it  will  move  espe- 
cially in  their  fibro-vascular  framework,  which  we  have 
seen  terminates  in  the  leaves  in  a  system  of  capillaries 
which  anastomose  with  each  other,  in  the  same  manner  as 
the  capillary  vessels  in  which  the  arterial  and  venous  sys- 
tems of  animals  terminate. 

The  motion  of  the  nutrient  fluid  in  the  animal  and 
vegetable  capillaries  is  mainly  to  be  attributed  to  local 
influences.  It  is  capable  of  being  proved  by  experiment, 
that  if  two  liquids  communicate  with  each  other  through 
a  capillary  tube,  for  the  walls  of  which  both  have  an 
affinity,  the  liquid  which  has  the  greatest  affinity  for  the 
tube  will  be  absorbed  into  its  cavity  and  drive  the  other 
before  it.  It  is  obvious  that  the  same  effect  will  take 
place,  if  instead  of  one  we  suppose  any  number  of  tubes  to 
communicate  in  this  manner.  If  now  we  suppose  that  the 
liquid  absorbed  into  the  tube  undergoes,  whilst  there,  such 
a  change  in  its  constituents  as  to  have  its  affinity  for  it 
diminished,  it  is  plain  that  it  may  be  driven  out  by  a  fresh 


100  THE  NUTRITIVE  FUNCTIONS. 

supply  of  the  original  fluid,  and  in  this  way  a  continual 
flow  of  the  fluid  in  the  same  direction  would  be  produced. 

Now  such  appears  to  be,  to  a  very  great  extent,  the 
nature  of  those  influences  which  govern  the  movements  of 
the  nutrient  fluid  in  the  capillaries  of  animals  and  plants. 
The  fluid,  for  example,  contains  certain  substances  which 
are  necessary  to  the  nutrition  of  a  certain  tissue,  and  it  is 
for  this  reason  attracted  into  that  tissue  to  which  it  imme- 
diately gives  up  the  nutrient  elements  required ;  this  neu- 
tralizes the  affinity  between  the  tissue  and  the  fluid,  and 
the  latter  is  consequently  driven  out  by  the  superior  at- 
traction then  possessed  by  the  tissue  for  a  fresh  portion  of 
the  fluid.  The  fluid  which  is  driven  out  of  one  part  may 
still,  however,  be  qualified  to  nourish  another  part  which 
requires  a  different  portion  of  its  elements,  and  between  it 
and  this  new  tissue  an  affinity  now  exists,  the  result  of  the 
loss  it  has  already  sustained,  which  did  not  exist  before; 
it  is  thus  drawn  into  the  fresh  tissue  and  repelled  from  it 
as  before,  by  the  entrance  of  a  fresh  supply,  and  in  this 
manner  the  current  moves  on  from  cell  to  cell,  through 
the  entire  capillary  network.  This  important  physiological 
law  was  first  developed  by  Professor  Draper 5*  and  seems 
to  afford  a  clear  and  satisfactory  explanation  of  the  motion 
of  the  nutrient  fluid  in  the  capillary  system  of  plants  and 
animals. 

That  the  motion  of  the  capillary  currents  in  animals  is 
induced  by  the  vital  processes  going  on  in  the  tissues,  and 
is  not  to  be  attributed  to  the  muscular  contractions  and 
dilatations  of  the  central  organs  of  circulation,  is  evident 
from  the  following  facts  : 


*  See  Draper  "  On  the  Forces  which  produce  the  Organization  of 
Plants." 


'  ;,: :  101 

A  careful  examination  of  the  capillary  circulation  in  the 
living  animal,  discloses  certain  irregularities  in  the  motion 
of  the  currents,  which  it  is  impossible  to  attribute  to  any 
other  than  local  influences,  or  the  alternate  attraction  and 
repulsion  of  the  fluid  by  the  tissues.  Sometimes  the  cur- 
rent is  rapid,  then  slow,  occasionally  it  stops,  or  its  direc- 
tion may  be  even  reversed. 

In  certain  diseased  states  of  the  body,  there  is  an  unusual 
amount  of  blood  in  the  capillaries  of  the  affected  part,  as 
is  evident  from  the  amount  of  local  inflammation ;  yet  the 
general  current  of  the  circulation  is  not  at  all  affected. 
This  movement  of  the  blood  into  the  capillaries  is  entirely  in- 
dependent of  the  heart's  action,  the  energy  of  which  is  not 
increased ;  it  therefore  depends  entirely  on  the  attraction 
exercised  on  it  by  the  cells  of  the  diseased  parts. 

Any  increase  of  energy  in  the  vital  processes  of  any 
part  of  the  organism,  shows  the  action  of  local  influences 
in  diverting  the  current  of  the  circulation  into  new  chan- 
nels. Thus,  the  development  of  the  uterus,  during  preg- 
nancy, induces  at  first  an  unusual  degree  of  activity  in  the 
capillary  circulation  of  those  parts ;  the  necessary  result  of 
the  changes  continually  taking  place  in  the  forming  tissues. 
An  increased  supply  of  blood  is  attracted  in  the  direction 
of  the  developing  organs  of  the  foetus,  and  there  is  a 
gradual  enlargement  of  the  diameter  of  the  arterial  trunk 
through  which  it  is  transmitted.  In  the  meanwhile,  the 
blood  continues  its  uniformity  of  flow  through  the  body. 
It  is  therefore  evident  that  these  organic  changes,  the 
result  of  the  increased  supply  of  the  blood  to  the  growing 
parts, v  take  place  independently  of  any  increase  in  the 
energy  of  the  action  of  the  heart. 

But  why  multiply  causes  unnecessarily?  Nature  is 
simple,  and  does  nothing  in  vain.  It  is  admitted  that  in 

9* 


OttlE  frtlT-IilTlVE  JUNCTIONS. 

both  animals  and  plants  the  vital  changes  take  place  in  the 
cells  situated  amongst  the  meshes  of  the  capillary  net- 
work, and  that  the  fibro-vascular  system  in  plants  and  the 
arterial  system  in  animals  are  merely  the  agents  employed 
in  the  transmission  of  the  fluid  to  these  cells,  which  are 
the  animal  and  vegetable  laboratories.  Therefore  the  mo- 
tion of  the  sap  and  blood  must  necessarily  originate  in  the 
forces  generated  by  the  nutritive  processes  carried  on  in 
these  cells,  in  the  different  parts  of  the  body.  There  must 
be  some  cause  to  induce  the  muscular  contractions  of  the 
heart,  those  successive  impulses  which  drive  the  blood  to 
the  remotest  parts  of  the  system,  and  it  seems  clear  that 
these  phenomena  have  their  origin  in  the  vital  processes 
which  are  continually  going  on  in  those  cells  with  which 
the  capillaries  finally  communicate. 

The  motion  of  the  blood  in  the  capillary  vessels  is  well 
seen  in  the  web  of  the  frog's  foot,  when  examined  with  a 
power  of  250  diameters.  The  blood-globules  are  seen  roll- 
ing along  in  single  and  double  file  through  the  minute 
capillary  ramifications. 

The  motion  of  the  sap  in  the  capillary  vessels  of  plants 
may  be  observed  in  those  in  which  it  is  more  or  less  dis- 
colored, and  rendered  opaque  and  milky,  by  the  presence 
of  floating  particles  of  resin,  caoutchouc,  and  other  sub- 
stances. It  was  first  observed  by  M.  Schultz,  of  Berlin, 
in  1820,  and  was  called  by  him  cyclosis,  in  reference  to 
its  circulatory  character,  and  latex  in  allusion  to  its  milky 
appearance. 

The  vessels  which  contain  the  latex  or  milk-sap,  are 
cylindrical  tubes  with  thin,  transparent  walls,  without  any 
appearance  of  transverse  partitions.  They  are  either  simple 
or  branched,  and  frequently  anastomose  among  themselves, 
forming  a  network  with  irregular  and  unequal  meshes. 


CIRCULATION.  103 

These  vessels  exist  in  most  monocotyledonous  and  dicoty- 
ledonous plants.  We  find  them  generally  in  those  vascular 
bundles  which  form  the  salient  lines  on  the  under  surface 
of  leaves,  designated  as  nervures.  They  are  also  found  in 
the  interior  bark.  In  monocotyledons,  we  meet  with  them 
in  the  vascular  bundles  developed  in  the  midst  of  the  cel- 
lular tissue  which  forms  the  mass  of  the  stem. 

The  latex  itself  is  usually  a  fluid  of  a  white,  yellow,  or 
reddish  color.  This  color  is  due  to  the  presence  of  opaque 
corpuscles  of  various  hues,  which  being  collected  together 
in  abundance  in  a  watery  and  transparent  liquid,  commu- 
nicate to  it  their  color,  just  as  the  blood  and  milk-globules 
give  to  those  liquids,  colorless  in  themselves,  the  red  and 
white  colors  by  which  they  are  characterized.  The  latex 
when  poured  out  by  itself  into  a  vessel,  behaves  like  the 
blood,  and  separates  into  two  parts ;  a  liquid,  colorless  or 
slightly  colored  brown,  and  a  solid  matter  forming  a  sort 
of  clot,  composed  of  colored  globules.  These  globules  con- 
sist of  various  matters  insoluble  in  water,  such  as  wax,  fatty 
matters,  and  caoutchouc. 

The  motion  of  the  latex  or  milk-sap  is  seen  in  a  young 
expanded  leaf,  it  may  be  in  a  sepal  or  a  petal,  still  adhering 
to  the  plant,  especially  when  it  contains  a  considerable 
quantity  of  colored  sap,  as  for  instance,  the  young  ex- 
panded sepal  of  Chelidonium  majus,  or  the  large  stipule 
which  encloses  the  terminal  bud  of  Ficus  elastica.  If  the  epi- 
dermis be  carefully  raised  without  injuring  the  vessels,  the 
nature  of  the  movement  will  be  perceived.  Similar  move- 
ments probably  take  place  in  the  anastomosing  capillary 
vessels  of  all  plants,  but  they  are  rendered  impercep- 
tible to  us  by  the  transparency  of  their  juices. 


104  THE  NUTRITIVE  FUNCTIONS, 


CHAPTER  VI. 

ON  THE  NUTRITIVE  PROCESSES  OP  RESPIRATION  AND 
ASSIMILATION. 

The  nutritive  fluid  which  circulates  through  the  tissues 
of  plants  and  animals,  requires  to  be  constantly  brought 
into  immediate  contact  with  the  oxygen  of  the  atmosphere, 
which  is  the  principal  agent  in  effecting  those  important 
changes  in  its  constituents,  by  means  of  which  it  is  ren- 
dered capable  of  ministering  to  their  nutrition  and  deve- 
lopment. For  this  purpose  plants  have  been  provided  with 
leaves  and  animals  with  lungs. 

The  sap  of  plants  is  aerated  by  means  of  their  vasiform 
and  tubular  tissues,  which  communicate  with  the  atmos- 
phere through  the  stomata  or  openings  in  the  epidermis  of 
their  herbaceous  and  green  parts. 

These  vessels,  contain  sap  during  the  first  period  of 
vegetable  activity  in  early  spring,  which  is  gradually 
displaced  by  air.  This  fact  is  easily  verified,  by  cutting 
under  water  a  young  green  shoot  which  has  put  forth  its 
leaves ;  little  bubbles  of  air  will  be  seen  to  issue  from  the 
orifices  of  these  tubes. 

Respiration  consists  essentially  in  the  evolution  of  car- 
bonic acid  and  the  absorption  of  oxygen.  The  process  is 
performed  both  by  animals  and  plants,  and  has  its  origin  in 
the  same  general  requirements. 

The  first  source  of  the  demand  for  oxygen,  common  alike 
to  plants  and  animals,  arises  out  of  those  changes  which  are 
always  going  on  in  their  interior,  as  a  part  of  their  nutrient 


RESPIRATION.  105 

operations.  It  is  often  said  that  plants  cannot  be  sustained 
on  organic  nutriment,  that  they  live  on  inorganic  matter, 
which  they  organize  as  food  for  animals ;  but  we  apprehend 
parasitic  plants  must  be  regarded  as  exceptional  cases; 
for  these  derive  their  nutriment  from  the  elaborated  juices 
of  the  plants  on  which  they  are  found,  and  not  at  all  from 
the  earth  and  atmosphere,  the  usual  sources  of  vegetable 
nutrition.  These  plants  contaminate  the  air  like  animals, 
absorbing  its  oxygen  and  giving  out  carbonic  acid.  This 
fact  is  so  well  known  and  established  that  it  will  not  be 
disputed.  It  is  sufficient,  therefore,  if  we  refer  to  the  ex- 
periments of  M.  Lory  upon  the  respiration  of  the  Oro- 
banchacese.* 

Oxygen  is  absorbed  and  carbonic  acid  evolved  in  ger- 
mination, at  the  birth  of  the  young  plant,  and  in  flower- 
ing, when  it  arrives  at  an  adult  state.  In  both  in- 
stances, starch  is  oxydized  and  converted  first  into  dextrine 
and  then  into  sugar,  for  the  nutriment  of  the  young  em- 
bryo, stamens,  and  pistils,  and  these  processes  are  accom- 
panied with  a  development  of  heat.  Both  the  embryo  and 
the  flower,  physiologically  considered,  may  be  regarded  as 
exercising  a  parasitic  action  on  the  organic  matter  pre- 
viously elaborated  for  them.  The  respiration  of  the  coty- 
ledonary  leaves  of  the  embryo,  and  of  the  corolline  envelope 
of  the  stamens  and  pistils  is,  in  every  respect,  a  true  oxyda- 
tion  or  combustion  of  the  store  of  saccharine  matter,  accom- 
panied by  the  evolution  of  carbonic  acid. 

It  is  true  that  plants,  with  the  exception  of  such  as  are 
parasitic,  live  on  mineral  matter,  which  they  convert  into 
organized  products;  but  the  organic  matter  which  they 
thus  create  is  not  available  for  the  development  either  of 

*  "Annales  de3  Sciences-Naturelles."  Botanique,  Sept.  1847. 


106  THE  NUTRITIVE  FUNCTIONS. 

their  own  organism  or  that  of  animals,  until  it  is  first  oxy- 
dized. 

Now  the  sap  is  digested  or  de-oxydated  in  the  leaves  of 
plants,  that  is  to  say,  the  carbonic  acid  of  the  sap  is  decom- 
posed under  the  influence  of  light,  and  all  the  superfluous 
oxygen  is  evolved  into  the  atmosphere.  The  remainder 
of  the  oxygen,  required  for  nutrition,  is  drawn  through 
the  vasiform  tissue  and  ducts  into  the  interior  of  the  plant. 
The  sap  in  all  parts  of  the  plant  is  thus  brought  into  com- 
munication with  the  gaseous  fluids  necessary  to  its  elabora- 
tion, and  those  various  organic  products  developed,  in  all 
of  which  oxygen  enters  into  composition  as  an  element. 
These  pneumatic  vessels  are  most  admirably  situated,  for 
this  purpose,  in  the  midst  of  the  woody  tissues  of  plants, 
through  which  the  sap  continues  to  flow  until  their  vital 
activity  ceases. 

The  sap  is  therefore  first  digested  or  de-oxydated  in  the 
leaves  of  plants,  and  the  food  is  changed  first  to  chyme  and 
then  to  chyle  in  the  stomach  and  intestines  of  animals,  res- 
piration or  oxydation  giving  the  finishing  change  to  the  sap 
in  the  interior  of  the  plant,  and  rendering  the  chyle  identi- 
cal with  the  blood.  Respiration  is  absolutely  essential  to 
the  growth  of  plants  as  well  as  of  animals. 

Dutrochet  ascertained  by  experiments,  that  the  air  con- 
tained in  the  ducts  and  spiral  vessels  in  the  interior  of  the 
stem,  was  altered  in  its  composition,  in  proportion  to  its 
distance  from  its  original  source  of  supply  in  the  leaves. 
He  found  that  the  air  in  these  vessels  was  gradually  de- 
prived of  its  oxygen,  which  was  absorbed  by  the  sap  in  the 
neighboring  vessels. 

That  the  interior  sap-cells  in  the  neighborhood  of  the 
air-tubes  absorb  oxygen  and  give  out  carbonic  acid,  is  evi- 
dent from  what  we  know  of  the  economy  of  those  opposite 


EESMRATION.  107 

changes  which  take  place  in  the  exterior  sap-cells  in  the 
parenchyma  of  the  leaves.  Recent  experiments  have 
shown  that  the  evolution  of  oxygen  gas  from  the  leaves  of 
plants  only  takes  place  when  the  sun  shines  directly  upon 
them  -j  that  the  process  ceases  when  his  rays  are  intercepted 
by  clouds,  and,  as  the  light  of  day  gradually  fades,  is  ac- 
tually reversed,  oxygen  being  absorbed  and  carbonic  acid 
eliminated.  Light  is  therefore  absolutely  necessary  to  the 
de-oxydizing  process,  which  varies  in  rapidity  with  the  dif- 
ferent degrees  of  illumination,  and  ceases  altogether  when 
this  influence  is  withdrawn,  oxydation  taking  place  during 
the  night.  ^Therefore  the  cells  in  the  interior  of  the  plant, 
in  proportion  as  they  are  withdrawn  from  the  solar  in- 
fluence by  intervening  layers  of  tissue,  must  necessarily 
become  more  and  more  absorbent  of  the  oxygen,  which  is 
communicated  to  them  through  the  air-tubes  from  the  leaf- 
laboratory,  and  the  air  in  those  tubes  must  also  become  im- 
pregnated with  carbonic  acid  in  proportion  to  the  amount 
of  tissue  which  they  have  traversed  in  the  dark  portions 
of  the  interior  of  the  plant. 

The  process  of  de-oxydation  or  digestion  in  the  leaves,  has 
masked  and  disguised  the  true  respiratory  process  in  the  in- 
terior of  plants,  which  is  carried  on  by  the  pneumatic  vessels 
of  their  fibro-vascular  system.  In  what  does  this  differ  from 
the  process  of  respiration  in  animals  ?  The  principle  is  pre- 
cisely the  same.  There  is  the  same  oxygenation  of  the  nutri- 
ent fluid  in  the  interior  of  both  organisms ;  but  the  sap  is 
oxygenated  in  the  plant  by  a  system  of  pneumatic  vessels 
which  officiate  as  conducts  of  oxygen  from  the  leaves,  and 
bring  it  into  direct  communication  with  the  sap-cells  in  all 
parts  of  the  vegetable  fabric ;  whereas  in  animals,  the  pneu- 
matic vessels,  which  oxygenate  the  blood,  are  confined  to 


108  THE  NUTRITIVE  JUNCTIONS. 

an  unique  and  special  organ  developed  in  one  part  of  the 
organism. 

Another  source  of  demand  for  oxygen,  common  to  both 
animals  and  plants,  arises  out  of  the  changes  which  arc 
always  going  on  in  them,  and  the  necessity  for  the  re- 
moval of  all  waste  matter  from  the  system,  Plants  are 
without  a  nervo-muscular  system,  and  are  therefore  ex- 
empt from  that  interstitial  waste  and  destruction  which 
takes  place  in  animals,  and  which  is  the  result  of  nervous 
and  muscular  action.  Although  they  have  no  organs  de- 
veloped expressly  for  the  removal  of  effete  matter,  we  never- 
theless see  them  spontaneously  throwing  off  those  parts  of 
their  fabric  which  are  no  longer  of  any  service  to  them. 
Thus  the  cotyledons  perish  as  soon  as  the  first  pair  of 
atmospheric  leaves  are  fully  developed;  the  bud-scales, 
which  protect  the  young  shoots  of  trees  through  winter,  are 
thrown  off  as  soon  as  spring  and  warm  weather  comes. 
The  blossoms  drop  from  the  trees  as  soon  as  they  have 
contributed  to  the  formation  of  their  fruits ;  and  the  trees 
themselves  shed  those  leaves  which  have  contributed  to 
their  nourishment  through  the  spring  and  summer  months, 
on  the  approach  of  winter,  because  their  vitality  is  ex- 
hausted, and  they  are  useless  to  the  plant.  In  all  these 
instances,  oxygen  is  absorbed  and  carbonic  acid  evolved. 
Thus,  in  both  animal  and  plant,  oxygen  is  the  principal 
agent  employed  in  the  removal  of  the  waste  matter.  Is  it 
objected  that  waste  matter  is  thrown  off  en  masse  from  the 
plant,  and  not  in  a  gaseous  condition,  as  in  the  animal  ? 
We  reply  that  the  evolution  of  waste  matter  in  the  gaseous 
form,  commences  with  the  ordinary  process  which  produces 
the  decay  of  leaves ;  their  decomposition  after  their  separa- 
tion is  only  a  continuation  of  the  same  process.  All  the 
waste  matter  thrown  out  of  the  animal  system  is  not  evolved 


ASSIMILATION.  109 

into  gases  before  it  is  eliminated,  but  only  a  part  of  it ;  the 
rest  appears  under  the  form  of  those  solid  and  liquid  fasces 
excreted  from  the  system  by  the  appropriate  organs,  and 
its  final  decomposition  takes  place  when  it  is  separated  from 
the  organism,  just  as  the  leaf  is  resolved  into  its  original 
elements  after  it  is  detached  from  the  branch.  We  cannot 
see  any  difference  except  in  the  greater  degree  of  its 
simplicity,  between  this  process  in  the  plant  and  in  the 
animal.  The  dead  matter  in  the  interior  of  the  organism 
is  of  service,  since  it  strengthens  the  fabric  of  the  plant, 
and  therefore  no  provision  has  been  made  for  effecting  its 
removal.  It  cannot  be  called  waste  matter.  It  is  other- 
wise with  the  foliage  and  flowers  with  which  plants  are 
annually  adorned.  These  cease  to  be  of  any  further  ser- 
vice as  soon  as  they  are  dead ;  they  are  therefore  separated 
from  the  plant  as  waste  matter. 

We  have  seen  that  plants  subsist  on  the  food  which  they 
find  in 'the  earth  and  atmosphere,  in  a  condition  suitable 
for  absorption  into  their  organism;  that  animals,  on  the 
contrary,  have  to  use  organs  for  the  prehension  and  the 
preparation  of  their  food  before  it  can  be  absorbed.  There 
is  the  same  simplicity  in  plants,  and  additional  complexity 
in  animals,  in  the  elimination  of  their  waste  matter ;  it  is 
thrown  off  at  once  from  the  plant,  but  in  animals,  a  special 
system  of  organs  has  been  superadded  to  the  general  organ- 
ism, in  order  to  effect  its  removal. 

ASSIMILATION  IN  PLANTS  AND  ANIMALS. 

The  food  of  plants  is  digested  and  rendered  nutritive 

in  their  leaves ;  that  of  animals  is  prepared  for  circulation 

in  their  stomach.     The  leaves  have  been  called  the  lungs 

of  plants,  and  the  process  of  respiration  has  been  repre- 

10 


110  THE  NUTRITIVE  FUNCTIONS. 

sented  as  consisting  in  the  absorption  of  the  carbonic  acid 
contained  in  the  air,  and  its  decomposition  under  the 
direct  influence  of  the  solar  light.  That  such  a  pro- 
cess does  go  on  in  the  leaves  is  undeniable.  The  carbon 
is  fixed  in  the  plant,  and  the  greater  part  of  the  oxygen  is 
exhaled  through  the  leaf-pores  into  the  atmosphere  ;  at  the 
same  time  it  is  evident,  from  the  nature  of  the  nutritive 
processes  going  on  in  the  interior,  and  the  intimate  connec- 
tion subsisting  between  the  duct-cells  and  the  leaves,  that 
some  of  the  oxygen  will  be  necessarily  absorbed  from  the 
leaves  into  the  interior  of  the  plant.  A  small  quantity  is, 
however,  amply  sufficient  to  supply  the  wants  of  vegetation, 
and  the  rest  is  poured  into  the  atmosphere  to  meet  the 
wants  of  animality.  It  is  therefore  true  that  carbonic  acid, 
which  is  given  off  from  the  lungs  of  animals  as  waste  matter, 
is  taken  in  by  the  leaves  of  plants ;  that  vegetables  purify 
the  air  which  animals  contaminate ;  that  what  is  poison  to 
us  is  food  to  plants.  It  is  also  true  that  the  leaves  are 
to  a  certain  extent  the  pulmonary  organs  of  plants,  because 
it  is  through  the  pores  on  their  surface  that  the  air  gains 
admission  by  means  of  which  the  fluids,  not  only  in  the 
leaves  but  in  the  interior  of  the  organism,  are  rendered  nu- 
tritious. Now  the  predominating  function  exercised  by  the 
leaves  is  unquestionably  that  of  de-oxydation  or  diges- 
tion, which  is  antagonistic  in  its  results  to  animal  respira- 
tion. When  we  speak  of  respiration  in  plants,  assuredly 
those  processes  in  which  oxygen  is  consumed  deserve  the 
name,  far  more  than  the  exhalation  of  oxygen  by  their 
leaves  and  other  green  parts. 

The  matters  contained  in  the  tissues  of  plants  are  very 
various,  and  are  either  solid,  liquid,  or  gaseous.  All  solid 
organic  matters,  such  as  starch  and  chlorophyl,  are  formed 


ASSIMILATION.  Ill 

by  de-oxydizing  processes,  the  fluid  contents  of  the  cells, 
such  as  gum  and  sugar,  chromule,  the  fixed  and  volatile 
oils,  organic  acids,  &c.,  are  the  results  of  oxydation.  Starch 
and  chlorophyl  are  therefore  the  products  of  vegetable  di- 
gestion, the  other  substances  of  vegetable  respiration.  This 
will  be  clearly  seen  if  we  consider  the  nature  of  these  sub- 
stances. They  are  of  great  importance  in  the  vegetable 
economy,  and  must  be  carefully  studied  if  we  would  obtain 
correct  views  of  the  nutrition  of  plants. 

Starch  is  one  of  the  most  abundant  and  useful  products 
of  vegetation.     It  exists  in  the  seeds,  roots,  and  stems  of 
plants,  and  in  the  pulp  of  fruits  ;  for  whilst  chlorophyl  is 
formed  only  on  the  outer  surface  of  plants,  starch  is  re- 
Fig.  22. 


a.  Club-shaped  granules  in  milky  juice  of  Euphorbia  splendens.    b.  Three 
of  the  lactiferous  vessels,  with  starch  granules  in  situ. — QUEKETT. 

stricted  to  their  interior,  light  being  absolutely  necessary 
in  the  one  case  and  darkness  in  the  other.  Starch  exists 
in  the  cells  of  plants  in  the  form  of  transparent  'and  color- 
less granules,  which  vary  in  figure  and  size  in  different 
species.  They  are  for  the  most  part  of  an  ovoid  shape ; 
but,  in  the  Euphorbiacese,  their  shape  is  like  an  elongated 


112  THE  NUTRITIVE  FUNCTIONS. 

dumb-bell  or  two-headed  club.  By  wounding  the  plant, 
and  placing  a  drop  of  the  milky  juice  under  the  micro- 
scope, these  singularly-formed  granules  may  be  easily  seen 
by  the  addition  of  a  little  tincture  of  iodine,  which  gives 
them  a  deep  blue  tinge.  Starch  granules  are  the  most 
easily  observed  in  the  cells  of  the  potato  where  they  are 
very  large.  On  the  application  of  tincture  of  iodine,  the 
starch  granules  are  readily  distinguished  by  the  deep  blue 
color  which  they  immediately  assume,  whilst  the  walls  of 
the  cells  in  which  th*ey  are  contained  remain  colorless. 
The  mode  of  their  formation  is  indicated  by  the  peculiar 
markings  on  their  outer  surface,  each  grain  having  a  spot 
at  one  end  which  is  called  the  hilum,  or  ostiole,  with  fine 
concentric  lines  drawn  around  it.  Sometimes  there  are 

Fig.  23. 


Grains  of  starch,  from  the  potato. 

two  or  three  ostioles  on  the  surface  of  the  same  granule. 
Occasionally,  crevices  are  seen  radiating  from  the  ostiole 
in  the  form  of  a  star,  which  open  more  or  less  profoundly 
into  the  interior  of  the  granule.  When  very  young,  the 
grain  of  starch  appears  as  a  vesicle,  with  a  perforation  in 
its  wall.  It  is  through  this  opening  that  the  matter  enters, 
by  a  movement  of  intussusception,  and  is  deposited  in 
successive  beds.  At  each  deposit,  the  vesicle  dilates  by  a 
kind  of  endosmotic  phenomenon,  until  it  finally  acquires 
a  degree  of  solidity  which  arrests  this  movement,  and  it  is 


ASSIMILATION.  113 

then  that  its  growth  ceases.  The  ostiole  is,  therefore,  not 
the  point  by  which  the  grain  of  starch  is  attached  to  the 
walls  of  the  cell,  but  it  is  the  cicatrice  of  the  canal  by 
which  the  matter  which  formed  the  successive  layers  pene- 
trated, in  a  state  of  solution.*' 

Physiologically  considered,  starch  is  unappropriated  cel- 
lulose, stored  up  in  this  particular  form  as  the  ready  pre- 
pared material  for  new  tissues ;  in  this  respect  it  performs 
precisely  the  same  office  in  the  organism  of  the  plant,  as  fat 
does  in  the  animal  economy.  Those  differences  in  ihe  life 
of  herbaceous  plants  which  has  occasioned  their  being  de- 
signated as  annuals,  biennials,  and  perennials,  results  from 
differences  in  the  quantity  of  the  starch  deposited  in  their 
roots.  The  roots  of  annuals  are  fibrous,  those  of  biennials 
and  perennials  are,  on  the  contrary,  thick  and  tuberous.  In 
the  first  instance,  all  the  starch  is  expended  in  the  forma- 
tion of  the  flowers  and  the  fruit,  the  act  of  reproduction 
exhausts  the  vital  energies,  and  the  entire  plant  perishes 
the  first  year ;  in  biennials  and  perennials,  on  the  contrary, 
only  a  portion  of  the  starch  formed  by  the  tissues  is  con- 
sumed the  first  year,  and  the  remainder  is  stored  up  in  the 
roots,  as  a  reservoir  for  the  growth  of  the  next  and  suc- 
ceeding years.  In  many  plants,  such  for  example  as  San- 
guinaria  Canadensis,  the  starch  accumulated  by  the  leaves 
through  the  summer  and  autumn  and  deposited  in  the 
rhizoma,  is  consumed  by  the  flowers  in  early  spring,  which 
appear  before  the  leaves. 

Chlorophyll  next  to  starch,  is  the  most  common  of  all 
the  cell  contents.  It  is  the  green  matter  of  plants,  and 
exists  in  all  those  parts  which  are  colored  green,  such  as  the 
leaves,  sepals,  and  the  bark  of  the  young  shoots.  It  forms 

*  See  "Precis  de  Botanique  et  de  Physiologic  Vegetale,"  &c.'  Par 
A.  Richard,  1852.  Premiere  partie,  pp.  10-11. 

10* 


114  THE  NUTRITIVE  FUNCTIONS. 

itself,  in  fact,  in  the  vitally  active  cells  on  the  exterior 
surface  of  plants  which  are  exposed  to  .the  light,  and  is 
wholly  absent  from  the  roots  and  from  the  interior  of  the 
stem,  to  which  the  light  cannot  gain  access.  Chlorophyl 
exists  in  the  cells,  in  the  form  of  separate  or  united  gra- 
nules, which  remain  either  stationary  and  united  to  the 
cell  walls,  or  float  freely  in  the  fluid  contents  of  their  cavities. 
These  granules  are  usually  of  a  globular  form,  and  may  be 
readily  distinguished  in  the  cells  of  the  liverworts  and 
mosses.  They  are  beautifully  apparent  in  the  little  lancet- 
shaped  leaves  of  Selaginella  apus,  a  common  but  never- 
theless very  interesting  moss-like  representative  of  the 
Lycopodiaceae. 

If  the  green  globules  of  chlorophyl  be  subjected  to  the 
action  of  iodine,  it  will  be  found  that  they  are  composed 
of  one  or  more  starch  granules,  invested  by  a  gelatinous 
layer  of  green  coloring  matter.  This  green  matter  be- 
comes colored  yellow  or  brown  by  the  iodine,  whilst  the 
granules  of  starch  take  the  blue  color  which  characterizes 
them,  and  appear  more  or  less  easily  and  with  a  purity  of 
tint  in  proportion  to  the  thinness  of  the  green  gelatinous 
layer  in  which  they  are  enveloped.  That  chlorophyl  is 
nothing  but  fecula  viridis*  or  green  starch,  is  further 
proved  by  testing  it  during  the  different  stages  of  its  deve- 
lopment. If  the  young  embryo  leaves,  formed  in  the  au- 
tumnal buds  of  the  horse-chestnut,  be  carefully  removed 
from  their  hybernaculum,  it  will  be  found  that  they  are  of 
a  pale-yellow  color  and  nearly  transparent.  If  iodine  be 
applied,  the  chlorophyl  granules  in  their  interior  will  as- 
sume a  deep  blue  tinge  which  shows  that  the  gelatinous 


*  See  "Outlines  of  Structural  and  Physiological  Botany,"  by  A. 
Henfrey,  page  19. 


ASSIMILATION.  115 

paste  which  envelopes  them  is  excessively  thin.  If  the 
leaves  be  examined  when  more  perfectly  developed,  the 
blue  tint  is  more  obscure,  because  the  gelatinous  bed  is 
thicker.  That  the  formation  of  this  green  gelatinous  en- 
velope is  posterior  to  that  of  the  starch  granules  which  it 
encloses,  is  evident  from  the  fact,  that  when  grains  of 
pure  starch  are  formed  in  organs  which  afterwards  become 
subjected  to  the  light,  they  become  covered  with  a  bed  of 
green  matter,  and  are  thus  converted  into  chlorophyl. 
Thus  potatoes  and  roots  will  assume  a  green  appearance  if 
the  earth  be  removed  from  them,  which  results  from  con- 
version of  the  starch  granules  into  chlorophyl. 

Gum,  or  rather  mucilage,  which  is  a  solution  of  gum,  is 
one  of  the  most  common  vegetable  products,  and  is  found 
plentifully  in  the  cells  of  all  young  and  growing  parts.  It 
is  one  of  the  forms  through  which  nutritive  matter  passes 
before  it  is  assimilated.  Glum  consists  of  C12H10010,  its 
chemical  composition  being  precisely  the  same  as  that  of 
starch.  It  is  in  the  form  of  gum  that  starch  passes  through 
the  walls  of  the  cells  in  which  its  granules  were  originally 
generated,  when  assimilated  by  the  plant.  From  the  bark 
of  many  trees,  gum  is  procured  in  the  form  of  an  exuda- 
tion. Two  well-marked  varieties  of  gum  have  been  distin- 
guished. Arabine,  soluble  in  cold  water,  and  constituting 
the  principal  ingredient  of  gum-arabic  procured  from  va- 
rious species  of  acacia;  and  cerasine,  insoluble  in  cold 
water  but  soluble  in  boiling  water,  constituting  the  gummy 
secretion  of  the  cherry  and  plum. 

Sugar  occurs  abundantly  in  the  sap  of  plants.  There 
are  two  marked  varieties  of  it.  Cane  sugar  procured  from 
the  sugar-cane,  sugar  maple,  beet,  carrot,  and  many  other 
plants ;  and  grape  sugar  occurring  in  numerous  fruits,  as 
grapes,  gooseberries,  currants,  peaches,  and  apricots.  Sugar, 


116  THE  NUTRITIVE  FUNCTIONS. 

though  sometimes  crystallized  as  an  excretion  in  the  nec- 
taries of  flowers,  yet  in  the  plant  exists  only  in  the  fluid 
state.  It  is  found  very  abundantly  in  growing  parts,  such 
as  buds,  germinating  cotyledons,  and  in  ripening  fruits. 

When  starch  passes  from  the  solid  to  the  fluid  state  it  is 
converted  into  gum  and  sugar.  This  transformation  is 
effected  by  means  of  a  vegetable  secretion  termed  diastase 
elaborated  for  this  purpose,  and  which  may  be  readily  ob- 
tained in  a  separate  state  from  the  neighborhood  of  the 
eyes  or  buds  of  the  pptato.  The  starch  thus  rendered 
fluid  is  called  dextrine,  which  is  conveyed  to  all  those 
parts  of  the  plant  where  growth  is  going  on.  In  flowering, 
the  starch  in  the  receptacle  of  the  flower  is  converted  into 
sugar,  as  nutritive  material  for  the  development  of  the 
pollen  granules  of  the  anthers  and  the  young  ovules  of  the 
germen;  whilst  that  portion  of  this  sugar  which  is  not 
required,  again  assumes  the  form  of  starch  in  the  cotyle- 
dons of  the  seeds,  to  be  once  more  reconverted  into  sugar 
for  the  nourishment  of  the  young  germ,  as  soon  as  its  vital 
activity  again  commences.  The  saccharine  matter  is  ela- 
borated by  organs  called  nectaries,  developed  for  this  pur- 
pose. This  sweet  juice  is  changed  to  honey  in  the  stomach 
of  the  bee.  It  is  the  food  of  the  bee,  which  is  furnished 
with  collecting  organs  for  the  purpose  of  removing  it  from 
the  plant. 

Volatile  and  fixed  oils. — The  volatile  or  essential  oils 
are  met  with  in  the  stem,  leaves,  flowers,  and  fruit  of  odo- 
riferous plants,  giving  them  by  their  volatility  their  pecu- 
liar odor.  These  oils  are  procured  by  distillation  along 
with  water.  They  are  called  essences,  and  contain  the  con- 
centrated odor  of  the  plants.  Thus  otto  or  attar  of  roses  is 
procured  from  the  petals  of  various  species  of  rose,  especi- 
ally Rosa  centifolia ;  oil  of  peppermint  from  the  leaves  of 


ASSIMILATION. 


117 


Mentha  viridis  ;  oil  of  lemons  and  oranges  from  the  rinds 
of  those  fruits;  oil  of  cloves  from  the  fruit  of  Caryophyllus 
aromaticus  ;  and  oil  of  turpentine  from  various  species  of 
Abies  and  Pinus.  Volatile  oils  are  generally  produced  and 
stored  up  in  certain  special  receptacles,  expressly  organized 
for  this  purpose.  They  are  represented  in 

Fig.  24. 


Vertical  section  of  the  rind  of  an  orange,  the  reservoirs"  of  volatile  oil  being 
marked  r,  r,  r.  The  cellular  tissue  of  the  rjnd  is  seen  surrounding  the  oil 
cavities,  and  the  cells  are  elongated  and  condensed  so  as  to  form  a  compact 
tissue  in  the  walls. 

The  transparent  dots  which  are  seen  in  the  leaves  of  the 
lemon,  the  orange,  and  the  myrtle  are  produced  by  these 
receptacles,  which,  being  filled  with  volatile  oil,  are  neces- 
sarily more  translucent  than  the  other  parts  of  the  leaves. 
When  held  up  to  the  light,  these  leaves  appear  as  if  punc- 
tured with  numerous  fine  holes.  Several  species  of  Hy- 
pericum  present  the  same  appearance. 

The  fixed  oils  are  found  chiefly  in  the  seeds  where  they 
supply  the  place  of  starch,  as  in  the  cotyledons  of  some 
of  the  Cruciferse,  Composite,  and  many  other  plants. 
Fixed  oils  are  generally  obtained  by  pressure.  Their 
economical  applications  are  very  numerous.  Olive,  almond, 
linseed,  rape,  cocoa-nut,  and  castor  oils  are  familiar  ex- 
amples. 

Such  are  the  facts  which  have  been  ascertained  respect- 
ing the  nature  of  these  vegetable  products.  Chlorophyl, 
starch,  gum,  and  sugar,  are  almost  universally  diffused; 


118  THE  NUTRITIVE  FUNCTIONS. 

the  other  substances,  including  the  different  organic  acids, 
are  restricted  to  certain  plants.  Here  we  must  stop,  for 
we  have  not  space  for  an  enumeration,  much  less  a  descrip- 
tion of  the  vast  variety  of  vegetable  products.  Almost 
every  plant  elaborates  from  the  sap  its  peculiar  solid,  fluid, 
and  gaseous  substances,  which  are  connected  in  some  way 
or  other  with  the  final  result  of  its  vegetative  acts,  the  de- 
velopment of  the  future  plant.  We  know  nothing,  com- 
paratively speaking  as  yet,  about  the  order  in  which  these 
substances  are  produced,  their  peculiar  chemical  relations, 
or  their  physiological  uses  to  the  plant.  The  subtle 
chemistry  of  the  cell-laboratory,  the  way  in  which  the 
cells  and  tissues  separately  work,  or  the  nature  of  that 
composite  influence  which  produces  the  future  germ, — all 
this  is  very  little  understood.  And  let  us  not  pride  our- 
selves on  our  knowledge  of  the  economical  uses  of  the 
various  vegetable  products.  Here  also,  science  is  in  its 
infancy.  Those  who  think  much  of  their  attainments,  or 
imagine  the  subject  ever  has,  or  ever  can  be  exhausted) 
have  never  yet  viewed  it  aright.  They  have  yet  to  learn 
the  limited  extent  of  human  knowledge  and  the  riches  and 
fecundity  of  nature.  The  finite  mind  can  never  fully  com- 
prehjend  the  works  of  an  Infinite  Being.  The  glorious  sun 
must  pour  all  his  rays  into  a  twinkling  star ;  the  illimitable 
ocean  be  comprehended  within  a  drop. 

It  would  seem  that  the  nutritious  portion  of  the  sap  not 
required  for  development,  is  deposited  in  the  cells  in  the 
form  of  starch,  which  substance  retaining  its  colorless  ap- 
pearance in  the  interior  of  the  plant  where  it  is  excluded 
from  the  light,  is  changed  into  chlorophyl  in  their  leaves, 
young  shoots,  and  other  superficial  parts  to  which  the 
light  has  free  access.  Chlorophyl  is  a  substance  closely 
allied  to  starch;  and' appears  to  be  equally  nutritious  to 


ASSIMILATION.  119 

the  plant ;  for  it  disappears  from  the  leaves  and  other  or- 
gans of  plants  when  their  vitality  is  exhausted.  A  partial 
oxydation  of  this  starch  produces  the  chromule,  and  as  the 
oxydation  increases,  gum  and  sugar.  This  oxydating  or  con- 
suming process  necessarily  partially  arrests  the  further  de- 
velopment of  the  organs ;  the  growth  of  the  plant  is  to 
some  extent  stopped,  the  petiole  assumes  the  form  of  a  fila- 
ment, and  the  lamina  being  contracted  into  an  anther,  a 
stamen  is  produced. 

The  change,  however,  from  the  de-oxydating  to  the  oxy- 
dating process  is  undoubtedly  gradual.  Hence  those 
transition  forms  between  the  leaf  and  stamen,  which  so 
satisfactorily  prove  that  the  two  are  but  one  and  the  same 
organ. 

We  have  already  shown  that  the  fibro-vascular  system 
of  plants  and  the  blood  vessels  of  animals  are  subordinate 
in  function  to  the  cells  with  which  their  terminal  capillary 
ramifications  finally  communicate,  and  that  it  is  in  these 
cells  that  the  changes  take  place  by  which  the  fluid  is  trans- 
muted into  the  various  products  necessary  to  the  nutri- 
tion of  the  organism.  The  sap  of  plants  in  traversing  the 
tissues  is  elaborated  into  starch,  chlorophyl,  chroinule, 
gum,  and  sugar;  and,  in  like  manner,  the  blood  which  is 
conducted  by  means  of  the  capillaries,  not  only  through  all 
the  softer  parts  of  the  framework,  but  even  into  the  solid 
substance  of  the  bones,  gives  up  its  constituents  to  the 
several  tissues  which  it  traverses,  the  cells  attracting  from 
it  their  own  proper  formative  material.  Its  constituents 
are  thus  transmuted  into  bile,  saliva,  tears,  and  various 
coloring  matters.  The  plumage  of  birds  and  the  hues 
of  flowers  are  alike  the  results  of  this  selecting  power  exer- 
cised by  the  cells  on  the  constituents  of  the  nutrient  fluid. 


120  THE  NUTRITIVE  FUNCTIONS. 

Assimilation  in  animals  is  therefore  as  plant-like  as  the 
rest  of  the  nutritive  processes. 

A  great  many  plants,  when  their  sap  has  been  digested 
in  the  leaves,  reject  at  their  exterior  various  matters  which 
are  often  condensed  and  solidified.  Thus  the  leaves  of  the 
sycamore  are  covered  with  a  saccharine  matter ;  the  stems 
of  pines  and  firs  exude  resins,  and  the  fruits  of  the  bay- 
berry  (Myrica  cerifera,)  are  coated  with  a  thick  vegetable 
wax.  In  these  instances,  the  plant  excretes  these  sub- 
stances which  are  the  products  of  nutrition,  but  which  are 
not  necessary  for  the  accomplishment  of  that  function. 
Their  appearance  is  the  result  of  their  superabundance  in 
the  subjacent  tissues,  the  distension  of  which  is  relieved 
by  this  exudation. 


PART   III 


REPRODUCTION  IN  PLANTS   AND 
ANIMALS. 


11 


CHAPTER  VII. 

GENERAL  CONSIDERATIONS    ON  REPRODUCTION  IN  PLANTS 
AND  ANIMALS. 

THE  nutritive  functions  of  digestion,  circulation,  and 
assimilation,  have  for  their  object  the  support  of  life,  by 
furnishing  to  organized  beings  without  ceasing,  new  and 
proper  materials  for  the  development  of  their  organs,  and 
the  reparation  of  the  waste  occasioned  by  the  movements 
of  anirnality.  But  it  is  the  nature  of  all  organized  beings 
to  have  but  a  limited  existence.  Their  organs  finally  lose 
the  faculty  of  sustaining  life,  and  the  cessation  of  their 
functions  brings  on  death.  All  the  organized  beings  exist- 
ing on  the  earth,  end  by  disappearing  from  its  surface ; 
and  their  races  would  speedily  become  extinct,  if  nature 
had  not  given  them  the  means  of  reproducing  and  multi- 
plying themselves. 

Through  reproduction  the  power  of  life  is  made  to  pass 
without  ceasing  into  other  bodies.  Our  parents  are  re- 
produced in  us  as  we  are  engendered  in  our  descendants. 
Thus  the  individual  perishes,  but  the  species  is  continued. 

Wherever  there  is  life,  there  is  attraction.  The  appear- 
ance of  matter  in  organized  beings  implies  a  draught  on 
the  resources  of  nature.  Each  germinating  seed  exercises 
a  special  attraction  on  the  earth  and  atmosphere,  and  dead 
inorganic  matter  collects  around  it,  to  be  embued  with 
vitality  and  moulded  into  an  organized  form. 

But  there  is  only  a  limited  amount  of  organizable  mate- 
rial existing  in  nature,  and  her  resources  would  therefore 
be  speedily  exhausted  were  there  not  an  equivalent  amount 


124          REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

returned.  The  matter  which  composes  the  bodies  of  ani- 
mals and  plants  is  only  "borrowed  from  the  earth  and 
atmosphere,  and  united  together  by  the  operation  of  natural 
laws  for  a  little  space  of  time."*  A  rotation  of  these  sub- 
stances is  therefore  absolutely  necessary. 

Wherever  there  is  death,  there  is  repulsion.  The  matter 
which  was  collected  by  life,  is  scattered  by  death.  The 
plant  or  animal  decays  and  disappears  from  our  sight. 
Both  are  alike  dissolved  by  the  repulsive  principle  into 
earthy  elements  and  invisible  gases/*and  the  atoms  held 
together  by  life  thus  sundered  by  death,  once  more  roam 
through  the  universe  and  gather  around  the  living  centres 
of  attraction,  to  be  again  re-moulded  anew  into  living  or- 
ganized forms. 

Matter,  whether  organized  or  inorganic,  never  perishes. 
Every  atom  bears  on  it  the  impress  of  its  everlasting  and 
infinite  Author.  If  it  disappears  from  observation,  it  is 
only  to  enter  into  new  combinations.  You  may  crush  the 
parts  of  a  body  to  powder,  melt  it  into  a  liquid,  or  by  a 
still  intenser  application  of  heat,  dilate  it  into  a  gas  and 
dissipate  it  in  vapor ;  but  it  still  exists,  and  in  many  in- 
stances can  be  collected  into  the  same  body  without  change 
of  form.  Mercury  and  water  may  be  converted  into  vapor, 
and  again  recovered  without  the  loss  of  a  single  particle. 
The  decay  of  animal  and  vegetable  bodies  is  only  a  process 
by  which  their  particles  are  liberated  to  assume  new 
forms. 

What  life  borrows,  death  will  sooner  or  later  claim. 
The  living  incur  a  debt  which  must  be  paid.  Matter  is 
the  grand  circulating  medium  of  nature,  and  all  that  is 
loaned  even  to  the  minutest  particle,  must  be  returned. 

*  See  the  author's  "  Principles  of  Botany  as  exemplified  in  the  Cryp- 
togamia,"  page  7. 


GENERAL  CONSIDERATIONS.  125 

Nothing  is  ever  lost  by  nature.  Death  is  the  agent  em- 
ployed to  enforce  the  claim,  and  we  must  surrender  what 
we  have  appropriated.  We  may  be  unwilling  to  pay  the 
debt,  but  in  this  instance  at  least  no  fraud  can  be  prac- 
tised. We  may  cheat  our  fellow-men  out  of  " their  own" 
but  nature,  NEVER. 

It  is  this  ceaseless  return  of  organizable  material  which 
keeps  up  the  continuity  of  the  stream  of  life  and  renders 
the  fountain  inexhaustible.  Hence  the  matter  of  which 
every  animal  and  vegetable  was  formed  in  the  earliest 
ages  is  now  in  existence.  We  ourselves  are  composed  of 
matter  as  old  as  the  creation ;  in  time,  we  must  suffer  in 
our  turn,  decomposition,  as  every  living  body  has  done 
before  us,  and  thus  resign  the  matter  of  which  we  are 
composed,  to  form  new  existences. 

The  reproduction  of  organized  beings  takes  place  in  a 
variety  of  ways.  We  have  already  described  the  gemmi- 
parous  and  fissiparous  modes,  which  take  place,  the  former 
among  compound  zoophytes,  and  the  latter  among  the  in- 
fusoria. These  two  modes  of  multiplication  require  no 
special  organs  for  the  formation  of  the  new  individuals, 
since  in  the  first  case  they  originate  on  all  the  points  of 
the  exterior  surface  of  the  body,  and  in  the  second,  it  is 
its  totality  which  divides  into  fragments,  each  becoming  a 
new  individual. 

But  it  is  not  in  this  manner  that  the  generality  of  plants 
and  animals  are  reproduced.  In  the  immense  majority  of 
cases  organized  bodies,  animals  and  plants,  reproduce 
themselves  by  means  of  fecundated  germs  which  we  call 
embryos.  These  embryos  form  in  a  particular  organ 
which  is  called  an  ovule,  in  consequence  of  receiving  from 
another  special  organ,  an  influence  which  impresses  on 
them  the  vital  movement,  or  in  other  words,  fecundates 
11* 


126  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

them.  The  organs  in  which  these  germs  are  developed, 
are  called  female  sexual  organs ;  the  organs  which  form 
the  matter  which  fecundates  them,  are  called  male  sexual 
organs. 

That  all  animals  are  produced  from  eggs,  omne  vivum 
ex  ovOj  is  an  old  adage  which  modern  researches  have 
abundantly  confirmed.  In  tracing  back  the  phases  of  ani- 
mal life,  we  invariably  arrive  at  an  epoch  when  the  inci- 
pient animal  was  enclosed  in  an  egg.  It  is  then  called  an 
embryo,  and  the  period  'passed  in  this  condition,  which  is 
more,  or  less  long  according  to  the  nature  of  the  animal, 
is  called  the  embryonic  period. 

Before  the  various  classes  of  the  animal  kingdom  had 
been  attentively  compared  during  the  embryonic  period,  all 
animals  were  divided  into  two  great  divisions ;  the  ovipar- 
ous, comprising  those  which  lay  eggs,  such  as  birds,  rep- 
tiles, insects,  and  mollusks;  and  the  viviparous,  which 
bring  forth  their  young  alive,  viz.,  the  mammalia.  This  dis- 
tinction has,  however,  lost  much  of  its  importance;  for  it  has 
been  ascertained  that  viviparous  animals  are  produced  from 
eggs  as  well  as  the  oviparous,  and  that  both  have  one  and 
the  same  uniform  structure  in  the  beginning.  In  vivipar- 
ous animals,  however,  the  eggs  undergo  their  early  changes 
in  the  body  of  the  mother,  that  is  to  say,  the  embryo  de- 
velops in  the  uterus,  and  bursts  the  membrane  of  the  egg, 
which  it  leaves  there,  coming  out  of  the  body  of  the  mother 
naked  and  already  formed ;  whereas  in  oviparous  animals, 
the  egg  is  laid  with  its  membranes  and  the  germ  which  it 
contains,  and  the  development  of  the  embryo  is  extra- 
uterine. 

Production  from  eggs  must  therefore  be  considered  as  a 
universal  characteristic  of  the  animal  kingdom.  Even 
animals  which  propagate  by  gemmiparous  and  fissiparous 


GENERAL  CONSIDERATIONS.  127 

reproduction,  also  lay  eggs.  The  former  are  only  additional 
means  employed  Iby  nature  to  secure  the  perpetuation  of  the 
species,  super-added  to  the  usual  method  of  propagation. 

Now  plants  have  sexes  or  sexual  organs  as  well  as  ani- 
mals.     The  female   sexual  organs  in  plants   are   called 


Fig.  24.  A  pistil  exhibited  in  section  to  show  the  young  ovules  d,  attached  to 
the  placenta  or  walls  of  the  ovary  a,  and  contained  within  its  cavity,  e.  The 
stigma  or  summit  of  the  pistil,  to  which  the  pollen  grains  adhere  when  fertiliza- 
tion takes  place.  &.  The  style  of  the  pistil,  through  the  loose  cellular  tissue  of 
which  the  pollen  tubes  descend  in  their  passage  to  the  ovary. 

Fig.  25.  A  stamen.  Its  filament  or  support  a,  and  its  anther  b,  discharging 
the  fecundating  matter  or  pollen. 

carpels.  The  pistil  which  consists  of  stigma,  style,  and  ger- 
men,  is  only  a  fully  developed  carpel.  The  male  sexual 
organs  are  named  stamens,  the  anthers  of  which  contain 
the  pollen  or  fecundating  matter.  The  stamens  and  car- 
pels are  the  essential  organs  of  reproduction  in  plants,  since 
it  is  by  the  mutual  action  of  these  bodies  that  the  vegetable 
embryo  is  formed. 

The  ovules  contained  in  the  germen  or  ovary  are  the 
bodies  which  after  impregnation  become  seed.  Their  exis- 
tence may  be  verified  by  making  a  section  of  the  germen, 
whilst  the  flower  is  still  in  the  bud,  and  before  the  anther 
cells  have  been  ruptured,  and,  in  this  condition,  they  un- 


128          REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

doubtedly  correspond  to  the  unimpregnated  ova  of  animals. 
The  line  or  ridge  on  the  interior  walls  of  the  ovary  to 
which  the  ovules  are  attached,  is  called  the  placenta.  The 
ovule  is  attached  to  the  placenta  either  directly  or  by 
means  of  a  prolongation  or  umbilical  cord,  termed  the  funi- 
culus.  The  ovule  when  fully  developed,  consists  of  a  coni- 
cally  shaped  nucleus  of  cells  containing  a  cavity,  termed 
the  embryo  sac,  in  its  interior.  This  nucleus  has  two 
coverings  which  have  no  organic  connection  with  each 
other  excepting  at  tne  base,  where  the  vessels  from  each 
covering  meet,  passing  through  the  funiculus  into  the  pla- 
centa, which  communicates  with  the  nourishing  walls  of  the 
germen.  This  common  point  of  union  is  called  the  chalaza. 
At  the  apex  of  the  ovule,  both  integuments  leave  an  open- 
ing which  has  been  termed  the  foramen  or  micropyle. 

The  reproductive  function  is  exercised  by  animals  and 
plants  when  they  have  attained  to  the  full  development  of 
all  their  parts,  or  arrive  at  an  adult  state.  The  period 
when  this  occurs  varies  greatly  in  each  species  and  depends 
entirely  on  the  peculiarities  of  its  constitution.  When  this 
epoch  arrives  in  plants,  a  visible  change  takes  place  in  the 
organic  functions ;  the  stem  ceases  to  elongate,  and  its 
internodes  no  longer  developing,  the  leaves  remain  crowded 
together  in  closely  approximated  whorls,  undergo  peculiar 
modifications  in  form  and  coloring,  and  a  flower  is  pro- 
duced. 

It  is  not  the  beauty  and  variety  of  the  hues  of  flowers, 
so  much  as  the  plan  on  wJiich  they  are  constructed,  which 
is  the  chief  point  of  attraction  about  them.  The  terminal 
rosette  of  leaves  called  the  flower,  so  different  in  size  and 
appearance  from  the  ordinary  leaves  of  the  stem,  is  simply 
metamorphosed  stem  leaves,  crowded  together  in  order  that 
they  may  act  on  each  other.  For  example,  all  must  have 


GENERAL  CONSIDERATIONS.  129 

noticed  the  folding  up  of  the  calyx  and  corolla  in  wet 
weather,  or  at  sunset.  The  function  exercised  by  the  two 
outer  whorls  of  floral  leaves  is,  in  this  case,  purely  protec- 
tive, and  the  design  of  their  close  proximity  to  the  stamens 
and  pistils  is  at  once  apparent ;  that  they  may  fold  over  the 
stamens  and  pistils,  and  thus  protect  them  from  the  effects 
of  the  night  dews  and  falling  rain,  which  would  otherwise 
act  injuriously  on  the  pollen  contained  in  the  cells  of 
the  anthers. 

Fig.  26. 


Fig.  26.  The  different  parts  of  a  flower,    a.  The  calyx ;  &.  the  corolla ;  c.  th« 
stamens ;  d,  the  pistils. 

The  reproductive  organs  of  plants,  popularly  called  their 
flowers,  are  commonly  the  most  showy  and  attractive  parts. 
To  this  rule,  however,  there  are  some  exceptions.  For 
example,  the  radicle  leaves  of  the  rattlesnake  plantain 
(Groodyera  pubesceus,)  one  of  the  North  American  Orchideae, 
found  in  shady  woods,  far  surpass  the  floral  leaves  in  the 
elegance  of  their  form  and  coloring.  This  plant  is  much 
prized  in  Europe,  and  is  cultivated  on  account  of  the 
beauty  of  its  foliage.  It  bears  a  spike  of  greenish  white 
flowers  of  a  very  ordinary  aspect ;  the  foliage  of  the  plant, 
on  the  contrary,  is  a  deep  rich  green,  most  beautifully 


180          REPRODUCTION  IN  PLANTS  AND, ANIMALS. 

reticulated  and  blotched  with  white,  and  retains  its  ver- 
dure through  the  winter. 

Among  animals  the  majority  of  species,  and  among 
plants  the  minority  are  unisexual,  or  dioecious ;  that  is  to 
say,  the  male  and  female  organs  of  generation  are  on  sepa- 
rate individuals  of  the  same  species. 

Difference  of  sex  is  much  more  marked  among  animals 
than  among  plants.  Among  insects  the  difference  of  sex 
is  readily  perceived,  not  only  by  a  difference  in  the  organs 
of  generation,  but  by  exterior  characters  which  are  easily 
recognized.  Thus,  in  general,  the  male  is  smaller  than 
the  female;  his  antennae  are  longer  and  better  formed; 
very  often  his  colors  are  more  lively,  his  mandibles  more 
powerful,  and  he  carries  on  his  head  or  his  thorax  appen- 
dages which  are  quite  wanting  in  the  female.  The  female 
insect  is  sometimes  apterous  or  provided  with  rudimentary 
wings,  whilst  those  of  the  male  are  fully  developed.  There 
is  no  such  marked  difference  between  the  sexes  in  dioe- 
cious plants.  The  Ailanthus  glandulosa  may  be  adduced 
as  an  illustration  of  this  uniformity  of  appearance.  With 
the  exception  of  its  peculiar  pollenic  odor  and  the  total 
absence  of  pistils  from  its  flowers,  the  male  tree  differs  not 
from  the  female  in  any  other  particular.  The  leaves  of 
both  plants  are  precisely  the  same  in  configuration  and 
surface.  The  male  and  female  trees  are  in  fact  so  exactly 
the  same  in  appearance,  that  it  is  utterly  impossible  to  re- 
cognize the  difference  of  sex,  except  at  the  epoch  of  flower- 
ing. We  are  not  aware  of  any  dioecious  plants  which  are 
an  exception  to  this  law  of  uniformity,  although  doubtless 
such  exist  in  nature. 

Unisexual  plants  are  apparently  not  so  favorably  situated 
for  sexual  intercourse  as  the  hermaphrodite  species,  where 
the  male  and  female  organs  are  present  in  the  same  flower. 


HYBRIDIZATION.  131 

The  pollen  or  fecundating  matter  is  however  wonderfully 
organized,  so  as  to  facilitate  its  action  on  the  pistils.  The 
granules  of  which  it  is  composed  are  so  small  and  nu- 
merous, that  they  form  a  fine,  light  powder,  which  is  easily 
transported  by  the  winds  to  a  very  considerable  distance 
from  the  plant.  Instances  might  be  cited  of  dioecious  trees, 
such  as  palms  and  pistachio  nuts,  the  females  of  which 
have  been  fecundated  by  pollen  from  male  trees  separated 
from  them  a  distance  of  several  leagues.*  The  wind 
drives  the  pollen  far  and  near,  and  the  air  becomes  some- 
times so  charged  with  it,  that  the  rain  in  falling  brings  it 
in  considerable  quantities  to  the  ground,  producing  the  so- 
called  sulphur  showers  of  which  we  read  about  in  history. 
There  is  no  doubt  also,  that  the  bee  and  other  insects  in 
search  of  honey,  convey  the  pollen  from  the  stamens  to 
the  pistils,  in  unisexual  plants. 

HYBRIDIZATION  IN  PLANTS  AND  ANIMALS. 

If  pollen  is  conveyed  by  means  of  the  atmosphere  and 
insects,  it  must  happen  that  plants  will  occasionally  hybri- 
dize, or  the  pollen  of  one  species  will  sometimes  fertilize 
the  ovules  of  another  species  of  the  same  genus.  The 
seeds  thus  produced  give  rise  to  individuals  of  an  inter- 
mediate character,  but  which  are  unable  to  perpetuate 
themselves ;  or  if  they  have  that  power,  lose  it  in  the  second 
or  third  generation. 

The  analogies  between  animals  and  plants  are  in  no  in- 
stances more  striking,  than  in  their  power  of  hybridizing, 
and  in  the  similarity  of  the  restrictions  imposed  by  all-pro- 
vident nature  on  the  exercise  of  this  function.  In  both,  it 

*  Precis  de  Botanique  et  Physiologic  Vegetale,  par  Achille  Richard, 
page  254.  1852. 


132  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

is  restricted  to  the  nearly  allied  species  of  the  same  genera, 
and  in  neither  case  is  the  hybrid  capable  of  perpetuating 
its  kind,  in  animals,  beyond  a  single  generation,  and  in 
plants,  beyond  the  second  or  third.  The  hybrid  vegetable 
if  reproduced  from  seed,  either  reverts  back  to  the  charac- 
ter of  one  of  its  parents,  or  becomes  sterile. 

Among  the  native  plants  of  North  America,  hybrids  are 
not  produced  to  that  extent  which  we  would  be  led  to  sup- 
pose. The  numerous  pollen  grains  of  different  species 
borne  on  the  wandering  winds  from  the  male  flowers  of  any 
particular  species  of  plant,  are  so  exactly  adapted  to  the 
female  flowers  of  the  same  species,  that  they  become  abor- 
tive on  "the  pistil  of  any  other  plant.  Hybrids  are  there- 
fore very  rarely  produced  by  wild  plants,  as  the  stigma  of 
any  particlar  species  of  plant  is  much  more  likely  to  attract 
the  pollen  of  its  own  stamens  than  that  of  other  plants.  The 
species  of  the  genus  Verbascum,  or  shepherd's  flannel,  a 
tall  plant,  very  common  along  road-sides,  with  a  leaf  not 
unlike  a  piece  of  flannel,  and  a  spike  of  yellow  flowers, 
show  a  greater  tendency  to  hybridize  than  almost  any  other 
species. 

Hybrids  are  much  more  common  among  cultivated  and 
domesticated  plants,  than  among  wild  ones.  It  is  a  fact 
well  known  to  cultivators  of  Ericas,  Pelargoniums,  Mesem- 
bryanthemums,  and  Stapelias,  in  the  green-house,  that 
when  several  species  of  any  of  these  genera  are  grown  to- 
gether, and  plants  are  raised  from  seed,  they  will  frequently 
turn  out  hybrids. 

It  is  the  constant  practice  of  gardeners  to  produce  the 
different  varieties  with  which  their  green-houses  are  adorned, 
by  conveying  the  pollen  from  one  plant  with  a  corolla  of  a 
certain  color,  to  the  pistils  of  another  plant  with  a  corolla  of 
a  different  hue.  The  seed  thus  generated  will  develop  a 


HYBRIDIZATION.  133 

plant  of  an  intermediate  shade  of  color.  This  principle  of 
cultivating  and  propagating  new  varieties  has  been  carried 
to  such  an  extent  by  florists,  among  certain  genera  that  are 
in  their  power,  that  the  original  species  can  now  scarcely 
be  distinguished.  Unfortunately  for  science,  if  a  slight 
variety  of  any  popular  flower  is  developed  by  this  hybridiz- 
ing process,  it  is  immediately  sought  after,  and  will  bring 
the  florist  a  higher  premium  than  some  newly  introduced, 
and  perhaps,  beautiful  exotic  species.  This  is  certainly 
very  bad  taste.  The  introduction  and  cultivation  of  new 
species  ought  to  be  encouraged,  because  it  is  of  far  more 
importance  than  the  breeding  of  hybrids.  We  should  be- 
come better  acquainted  with  exotic  flowers,  and  many 
undiscovered  and  valuable  properties  would  doubtless  be 
brought  to  light  in  some  of  them,  by  that  watchful  and 
studious  attention  to  their  habits  which  would  be  required 
for  their  successful  cultivation.  The  numerous  and  beauti- 
ful homes  of  wealthy  citizens  would  no  longer  be  surrounded 
by  gardens  filled  with  common  flowers,  but  we  should  find 
in  them  what  is  far  more  becoming,  select  and  choice  col- 
lections of  foreign  plants. 

Nearly  allied  plants  of  the  same  genus  can  alone  be  made 
to  hybridize.  Thus  the  different  species  of  the  lily,  straw- 
berry, and  the  geranium,  intermix  freely  with  the  indivi- 
duals of  the  same  genus ;  but  the  lily  and  strawberry,  two 
different  genera,  cannot  be  made  to  fertilize  each  other. 

To  the  facility  with  which  the  species  of  some  genera 
hybridize,  are  we  indebted  for  all  the  splendid  varieties  of 
the  rose,  dahlia,  and  geranium.  These  can  only  be  propa- 
gated by  cuttings,  or  by  offsets  or  portions  of  the  root. 

The  study  of  the  laws  of  hybridization  is  important,  as 
connected  with  the  origin  and  limitation  of  species.     If,  as 
some  authors  believe,  there  are  only  a  few  original  species, 
12 


134          REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

and  all  the  rest  are  the  result  of  hybridization,  then  there 
is  no  limits  to  species  and  no  permanence  whatever  in  their 
characters.  This,  however,  is  not  borne  out  by  facts.  It 
is  necessary  in  order  to  conception,  not  only  that  the  pollen 
or  sperm  should  reach  the  vegetable  or  animal  ovule,  but 
also  that  there  should  be  some  harmony  of  relation  between 
the  germ  and  the  nature  of  the  fecundating  element,  other- 
wise vivification  will  not  ensue.  Thus,  notwithstanding  the 
mixture  of  the  fluid  of  the  milt  of  different  male  fishes  in 
the  same  waters,  where  there  are  dispersed  so  many  different 
species  of  eggs,  hybrids  amongst  them  are  rare;  in  like 
manner,  each  dioecious  plant  develops  only  on  the  stigmas  of 
its  pistils,  the  pollen  of  its  true  species,  from  amongst  so 
many  other  kinds  of  pollen  carried  by  the  same  winds.  It 
is  thus  that  the  character  of  each  species  is  perpetuated  in 
its  native  purity. 

Most  plants  are  hermaphrodite,  that  is  to  say,  the  male 
and  female  are  united  in  the  same  individual.  Thus  in  the 
majority  of  flowers  the  stamens  surround  the  pistils  on  a 
common  support,  as  in  the  lily  and  geranium,  or  they  may 
be  developed  apart  from  each  other,  in  separate  flowers  on 
the  same  plant,  as  in  the  Indian  corn  and  mock-orange. 
In  this  last  instance  the  plants  are  said  to  be  monoecious. 
Some  animals  are  also  hermaphrodite,  such  as  muscles,  oys- 
ters, zoophytes ;  in  fact,  among  all  the  immovable  mollusca 
and  radiata  which  approach  so  closely  in  functions  and 
habits  to  plants,  hermaphrodisni  prevails,  which  is  the  most 
common  manifestation  of  sexuality  in  the  vegetable  world. 


FECUNDATION.  135 


CHAPTER  VIII. 

ON  THE  ESSENTIAL  AND  CONSECUTIVE  PHENOMENA  OF 
REPRODUCTION. 

The  process  of  fecundation  appears  to  be  as  follows : 
As  soon  as  the  calyx  and  corolla  are  expanded,  the  stamens 
free  from  all  confinement  take  a  rapid  development,  and 
the  anthers  up  to  this  time  unruptured,  moist,  and  closed, 
become  dry,  and  opening  their  cells,  discharge  the  pollen 
over  the  stigmar,  and  very  frequently  over  the  other  parts 
of  the  flower.  The  stigma,  or  apex  of  the  pistil,  is  about  this 
time  bedewed  with  a  clammy  fluid,  which  serves  to  retain 

Fig.  27. 


Triangular  pollen  grain  of  the  evening  primrose,  (QSnothera,)  with  one  pollen 
tube  t,  protruded.  This  tube  is  formed  by  the  intine,  which  is  also  seen  pro- 
jecting at  the  other  angles. 

the  grains  of  pollen  on  its  surface.  The  grains  of  pollen, 
after  remaining  for  some  time  on  the  humid  stigma,  absorb 
its  moisture,  and  are  seen  to  swell,  so  that  those  which  are 


136  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

elliptical  assume  a  spherical  form.  A  few  hours  contact  is 
all  that  is  necessary  to  produce  this  change  in  some  species, 
whilst  many  days  are  required  for  others.  The  swelling  in- 
creases, until  at.  last  the  thin  and  highly  extensible  intine,  or 
inner  coat  of  the  pollen  grain,  is  pushed  through  one  of  the 
pores  or  ostioles  in  the  surface  of  extine  or  outer  coat,  the 

Fig.  28. 


Longitudinal  section,  of  the  pistil  of  Helianthum  denticulatum,  showing  the 
ovules  in  the  interior  of  the  ovary  attached  to  the  placenta,  by  means  of  the 
funiculus,  or  vegetable  umbilicus ;  b,  style ;  c,  stigma ;  a,  pollen  granules,  the 
tubes  of  -which  have  descended  the  style  and  entered  the  micropyle  of  the 
ovules. 


FECUNDATION.  137 

mode  of  debiscence  being  always  determined  by  the  nature 
of  that  surface.  This  pollenic  tube  penetrates  the  loose 
cellular  tissue  of  the  stigma,  grows  downward  through  the 
central  portion  of  the  style,  and  having  arrived  at  its  base, 
enters  the  germen  or  ovary,  in  which  the  ovules  are  found 
up  to  this  period  unfertilized.  The  pollen  tube  enters  one 
of  the  unimpregnated  ovules  through  the  micropyle,  pene- 
trating the  tissue  of  the  nucleus  till  it  reaches  the  embryo 
sac.  Fecundation  appears  to  be  produced  by  the  simple 
contact  of  the  pollen  tube  with  the  embryo  sac,  and  the 
imbibition  by  the  embryonal  vesicle  of  the  contents  of  the 
pollen  grain  through  the  intervening  membrane,  the  fluid 
contents  of  the  two  cells  being  thus  commingled.  The 
fluid  matter  of  the  pollen  grain  is  called  fovilla,  and  its 
flow  through  the  pollen  tube  is  easily  perceived  by  the 
movements  of  those  microscopic  corpuscles  which  it  con- 
tains. 

The  pollen  tubes  may  be  readily  inspected  under  the 
microscope  in  many  plants,  and  in  none  more  readily  than 
in  the  Asclepias,  or  Milkweed.  In  that  family  the  pollen 
grains  cohere  together  in  masses  termed  pollinia,  and  their 
united  tubes  being  protruded,  are  consequently  of  such  a  size, 
as  to  be  readily  perceived  by  a  moderate  magnifying  power. 

The  young  ovules  which  are  attached  to  the  placenta 
or  wall  of  the  germen,  before  the  flower  opens,  con- 
tinue to  grow  until  that  time,  but  no  longer,  unless  they 
are  acted  upon  by  the  pollen  of  the  anthers.  The  neces- 
sity for  this  process  shows  why  it  is  that  stamens  and  pis- 
tils are  so  frequently  found  together  in  flowers,  and  why 
the  former  surround  the  latter  so  nicely  as  they  in  general 
do;  and,  in  circumstances  which  are  apparently  adverse 
to  fertilization,  the  admirable  contrivances  to  bring  about 
the  same  end.  Thus,  in  pendulous  and  upright  flowers, 
12* 


138  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

the  filaments  of  the  stamens  and  the  style  of  the  pistil  are 
so  developed,  as  to  bring  the  anthers  and  stigma  into  the 
most  favorable  relative  position  for  communicating  with 
each  other.  This  is  beautifully  exemplified  in  the  ladies 
ear-drop  (Fuschia,)  which  is  a  pendulous  of  drooping  flower. 
The  style  of  the  pistil  is  considerably  elongated,  and  the 
filaments  of  the  stamens  are  short,  so  that  the  anther 
cells  are  necessarily  situated  above  the  pistil,  in  order  that 
its  viscid  stigma  or  summit  may  receive  the  pollen  as  it 
falls  out  of  them.  In  upright  flowers,  on  the  other  hand, 
we  have  a  reverse  arrangement  of  the  parts ;  for  the  style 
of  the  pistil  is  in  a  great  measure  suppressed,  and  the  fila- 
ments of  the  stamens  are  so  developed  as  to  place  the 
anthers  above  the  stigmatic  surface. 

The  ovules  having  received  the  impregnating  matter,  the 
pollen  tubes  wither  from  above  downwards,  the  foramen  or 
micropyle  of  the  ovules  closes,  embryos  .or  miniature  plants 
begin  to  form  in  them,  and  they  are  gradually  transformed 
into  seeds.  The  ovary  or  cavity  of  the  pistil  containing  the 
ovules,  gradually  swells  under  these  influences.  Enlarged 
and  ripened,  it  constitutes  the  pericarp  or  seed  vessel. 

While  the  fruit  enlarges,  the  sap  is  drawn  towards  it,  and  a 
series  of  changes  soon  announce  that  a  new  vitality  is  estab- 
lished in  the  impregnated  parts  to  the  detriment  of  the  others. 
The  flower,  beautiful  up  to  this  moment,  and  adorned  with  the 
most  lively  colors,  loses  its  pleasing  aspect.  The  petals  fade 
and  fall.  The  stamens,  having  fulfilled  their  functions, 
prove  the  same  degradation.  The  stigma  and  style  of  the 
pistil  being  now  useless  to  the  plant,  disappear  equally  with 
the  other  parts.  The  germen  alone  remains  in  the  centre 
of  the  flower,  and  swells  into  a  fruit  abounding  with  seed 
by  which  the  species  is  continued.  It  is  not  an  unusual 
thing  to  see  the  calyx  persistent  with  the  germen,  and 


DEVELOPMENT  OF  THE  OVULES.  139 

contributing  along  with  the  green  walls  of  the  pericarp 
or  seed  vessel  to  the  nourishment  of  the  young  embryo. 
The  vitality  of  all  the  organs  of  the  flower  is,  however,  ex- 
hausted in  succession  before  the  seed  arrives  at  maturity 
and  the  embryo  is  fully  developed;  the  calyx  and  pericarp 
alike  perish,  when  they  have  fulfilled  this  the  last  and  most 
important  function  of  vegetable  life.  An  attentive  observer 
may  watch  these  changes  throughout  the  summer  months, 
in  any  plant  that  produces  flowers  and  fruit,  and  may  thus 
satisfy  himself  of  the  general  correctness  of  these  state- 
ments. 

At  the  period  of  flowering,  a  great  exhaustion  of  the  nu- 
tritive juices 'of  plants  invariably  takes  place.  In  annual 
herbaceous  plants,  the  formation  of  the  seed  not  only  ex- 
hausts the  vitality  of  the  flower,  but  of  the  stem  and  leaves, 
and  the  whole  plant  perishes  the  first  year.  In  biennials, 
a  store  of  nutritive  matter  is  assimilated  during  the  first 
year,  which  is  deposited  in  the  root,  and  consumed  by  the 
act  of  flowering  the  second  year;  the  plant  therefore  neces- 
sarily perishes.  In  perennial  herbaceous  plants,  which 
invariably  rise  from  an  underground  stem,  the  aerial  portion 
of  the  plant  always  dies  down  to  the  ground  at  the  close 
of  the  flowering  season ;  but  the  subterranean  part  remains 
alive  through  winter,  and  as  invariably  re-appears  above  the 
ground  in  spring ;  therefore,  only  the  upper  part  of  such 
plants  is  exhausted  in  flowering.  But  in  woody  perennials, 
the  formation  of  the  flowers  and  fruit  consumes  only  the 
nutriment  contained  in  the  peduncle  and  its  immediate 
supports ;  but  the  rest  of  the  plant  is  not  injured.  The 
first  and  succeeding  year's  growth  of  stem  is  therefore  per- 
sistent, or  remains  alive  above  the  ground.  It  is  true  that 
the  tree  sheds  its  summer  leaves,  and  spreads  its  naked 
branches  to  the  wintry  sky ;  but  the  stem,  the  numerous 


140  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

branches  and  branchlets  of  the  naked  tree  are  not  dead. 
Life  exists  all  along  the  central  axis,  and  is  lying  in  the 
bud  or  hibernaculum  of  the  young  shoot,  in  a  dormant 
state,  till  spring  awakens  it  to  a  new  existence.  Hence  it 
is,  that  every  year,  a  plant  with  a  ligneous  persistent  stem 
increases  in  altitude,  until  it  becomes  a  shrub  or  tree  with 
a  noble  canopy  of  foliage.  Such  may  be  fairly  considered 
as  the  highest  developments  of  vegetable  matter. 

The  term  fruit  has  a  more  extended  signification  in  botany 
than  in  ordinary  language.  It  is  applied  to  the  full  grown 
ovary  or  pericarp,  whatever  may  be  its  size,  form,  color,  or 
texture,  and  whether  it  is  edible  or  not.  A  grain  of  wheat 
or  corn,  or  the  pericarp  of  a  sunflower  or  thistle,  considered 
botanically,  is  as  truly  a  fruit  as  a  peach,  a  gooseberry,  or 
a  melon. 

Sometimes  the  texture  of  the  fruit  or  pericarp  remains 
nearly  the  same  as  at  first,  or  it  may  grow  into  a  fleshy  body, 
which  gradually  changes  into  an  agreeable  pulp,  as  in  the 
grape.  Occasionally  the  pericarp  becomes  crustaceous  and 
woody  in  its  structure,  as  in  the  nut ;  or  it  may  become  in 
part  hard  and  dry,  like  a  nut,  and  in  part  a  delicious  pulp, 
as  in  the  plum  and  peach. 

There  are  few  plants  in  which  all  the  ovules  become  per- 
fect seeds.  Many  are  suppressed  during  their  progress  of 
growth,  so  that  frequently  one  seed  is  developed  at  the  ex- 
pense of  several  ovules.  This  is  well  seen  in  the  prickly 
pericarp  of  the  chestnut,  (Castanea  vesca,)  which,  when 
ripe,  opens  by  four  valves,  and  drops  the  one  or  two  nuts 
contained  in  its  interior.  In  the  ovary  of  the  chestnut 
there  are  usually  fourteen  ovules.  Most  of  these  how- 
ever become  abortive,  or  perish  as  the  ovary  ripens  into 
the  pericarp ;  whilst  such  as  remain  are  generally  very  much 
reduced  in  size,  one  or  two  nuts  growing  at  the  expense  of 


DISPERSION  OF  SEED.  141 

the  rest,  and  filling  the  whole  cavity  of  the  pericarp.  When, 
however,  the  embryo  is  fully  developed  within  it,  the  ovule 
becomes  the  seed,  and  the  ovary  the  fruit.  The  seed  is 
detached  from  the  parent  plant,  and  the  life  which  has  passed 
away  from  the  other  parts  in  succession,  now  lies  dormant 
within  its  folds. 

The  separation  of  the  seed  at  maturity  from  the  parent 
plant  may  be  regarded  as  the  parturition  of  the  plant. 
Sometimes  the  pericarp  or  seed-vessel  opens  with  a  spring- 
like mechanism,  and  the  seeds  are  thrown  to  some  con- 
siderable distance.  The  pericarp  of  the  common  garden 
balsam,  (Impatiens,)  and  that  of  the  castor  oil  plant,  (Ri- 
cinus,)  may  be  given  as  illustrations.  When  the  pericarp 
or  seed-vessel  does  not  open  elastically,  and  the  seeds  re- 
main attached  to  its  walls,  the  atmosphere  sometimes  frees 
them  from  their  confinement.  We  see  every  day  the  wind 
transporting  the  seeds  of  plants  which  have  developed  little 
feathery  appendages,  contrivances  evidently  intended  to 
catch  the  breeze,  by  means  of  which  they  are  detached  from 
the  pericarp  and  carried  often  to  a  great  distance  from  the 
parent  plant.  Neither  is  there  any  mistaking  the  intention 
of  nature  in  furnishing  the  seeds  of  some  plants  with  barbs 
or  hooks,  by  means  of  which  they  adhere  to  the  dress  of  the 
passing  traveller,  who  thus  unconsciously  becomes  the  in- 
strument in  effecting  their  removal.  In  the  autumnal 
months,  all  persons  must  be  familiar  with  seeds  which,  thus 
furnished,  have  attached  themselves  to  their  dress,  and 
forced  themselves  on  their  attention.  The  seeds  of  the 
Spanish  Needles,  (Bidens  bipinnata,)  are  in  this  respect, 
particularly  troublesome. 

If  the  seed,  thus  separated  by  any  of  these  agencies,  is 
favorably  located,  all  is  quiet  until  the  return  of  suitable 
conditions  of  temperature,  air,  and  moisture,  when  the  vital 


142  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

movements  of  life  again  commence  those  impulses  which  it 
received  from  the  parent  plant.  Th&  chick  bursts  through 
the  egg,  impatient  of  confinement,  and  the  embryo  plantule 
ruptures  the  integuments  of  the  seed,  running  through  the 
same  phases  of  development  as  the  plant  on  which  it  origi- 
nated. 

As  soon  as  the  seed  begins  to  germinate,  the  first  thing 
that  we  notice  is  the  softening  and  swelling  of  its  envelopes ; 
its  testa  or  outer  covering  is  ruptured,  and  the  embryo  elon- 
gates downwards  by  its  radicle  or  young  root,  and  upwards 
by  its  plumule  or  young  stem,  lifting  the  cotyledons  or  seed 
leaves  above  the  earth's  surface.  These  seed  leaves,  when 
exposed  to  the  light,  speedily  acquire  a  green  hue,  and  in 
dicotyledonous  embryos  ultimately  assume  the  form  of  two 
opposite  leaves.  These  leaves  are  somewhat  thick  and 
fleshy,  their  margin  is  invariably  entire,  and  they  ulti- 
mately become  so  altered  in  appearance,  as  to  be  altoge- 
ther different  from  what  they  were  when  wrapped  up 
within  the  folds  of  the  testa.  If  the  plant  has  but  one  of 
these  leaves,  it  is  called  a  Monocotyledon,  if  it  has  two,  a 
Dicotyledon.  Plants  that  spring  up  without  these  appen- 
dages are  called  Acotyledons.  These  last  develop,  not  from 
seeds,  but  spores. 

The  cotyledonary  leaves  attached  to  the  embryo  contain 
a  store  of  starch,  which  contributes  to  the  development  of 
the  first  pair  of  atmospheric  leaves  and  also  to  the  extension 
of  the  root  in  the  soil ;  hence,  at  the  end  of  a  certain  time 
they  fade  and  fall,  having  discharged  their  allotted  func- 
tions. The  second  pair  of  leaves  take  the  form  peculiar  to 
the  plant  and  remain  permanently  attached  to  its  stem ;  as 
they  aerate  the  fluid  absorbed  into  the  interior  of  the  plant 
by  the  radicles,  much  more  perfectly  than  the  cotyledon- 


GERMINATION.  143 

ary  leaves  did,  the  growth  of  the  plant  is  necessarily  more 
rapid. 

It  is  important  then  to  take  all  possible  means  of  favor- 
ing the  growth  of  the  second  pair  of  atmospheric  leaves. 
As  the  power  of  absorbing  food  from  the  atmosphere  and 
soil  increases  with  every  fresh  growth  of  leaves  and  fibres, 
and  is  necessarily  very  feeble  in  the  beginning,  when  the 
plant  is  in  the  cotyledonary  stage  of  development,  it  is  ob- 
vious that  the  beds  must  be  kept  carefully  weeded,  and 
where  the  young  plants  are  very  much  crowded  together, 
the  feebler  must  be  removed,  in  order  to  encourage  the 
growth  of  such  as  are  more  vigorous. 

Perennial  plants  lose  their  sexual  organs  when  they  have 
served  them  but  once,  and  develop  others  each  year ;  but 
vertebrated  animals,  such  as  mammalia,  and  birds,  pre- 
serve those  with  which  they  are  provided.  In  all  the  in- 
ferior orders  of  animals,  these  organs  have  their  times  of 
repose  and  periods  of  activity. 

"  The  period  of  ovulation  is  to  animals  what  flowering  is 
to  plants }  and,  indeed,  few  phenomena  are  more  interesting 
to  the  student  of  nature  than  those  exhibited  by  animals  at 
the  pairing  season.  Then  their  physiognomy  is  the  most 
animated,  their  song'  the  most  melodious,  and  their  attire 
the  most  brilliant.  Some  birds  appear  so  different  at  this 
time,  that  zoologists  are  always  careful  to  indicate  whether 
or  not  a  bird  is  represented  at  the  breeding  season.  Similar 
differences  occur  also  among  fishes  and  other  animals  whose 
colors  are  then  much  brighter.  "*  Thus  in  early  spring, 
when  plants  put  forth  new  leaves  and  flowers,  we  have  re- 
newed at  the  same  time  the  hair,  feathers,  scales,  horns, 
and  other  external  appendages  of  animals.  Both  are  alike 

*  Principles  of  Zoology,  by  Louis  Agassiz. 


144  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

re-clothed.  It  is  the  season  of  love  and  happiness.  All 
nature  rejoices.  To  many  organized  beings  it  comes  only 
once.  In  this  respect  many  animals  are  like  annual  plants, 
perishing  as  soon  as  they  have  given  birth  to  their  eggs. 
The  lives  of  insects  especially  are  thus  limited. 

The  cause  of  this  grand  revolution  of  the  exterior  of 
organized  beings,  results  from  the  antecedent  restraint  of 
their  functions  by  the  cold  of  winter.  The  vital  properties 
of  the  tissues  of  animals  and  plants  are  still  retained, 
although  neither  may  exhibit  any  outward  indications  of 
life.  As  the  temperature  of  the  air  declines  to  the  freezing- 
point,  the  movements  of  life  either  cease  altogether  or 
become  quite  imperceptible ;  but  when  the  temperature 
again  rises,  the  usual  activity  of  the  plant  and  animal 
returns. 

There  are  different  degrees  of  torpidity  in  both  animals 
and  plants.  Some  animals  retire  into  situations  favorable 
to  the  retention  of  their  warmth,  and  occasionally  awaken 
in  mild  weather  and  apply  themselves  to  the  store  of  food 
which  they  have  previously  accumulated  in  autumn.  In 
other  species,  there  is  an  accumulation  of  fat  in  the  body 
of  the  animal  which  keeps  up  its  temperature  above  that  of 
the  surrounding  air.  These  animals  may  be  roused  from 
their  torpidity  into  which  they  soon  fall  again ;  their  re- 
spiratory movements,  though  diminished  in  frequency,  are 
still  continued.  But  in  the  Marmot  and  other  animals 
which  hibernate  completely,  the  heat  of  the  body  almost 
entirely  accords  with  that  of  the  surrounding  air,  being 
seldom  more  than  one  or  two  degrees  higher.  The  respi- 
ratory movements  fall  from  500  to  14  per  hour,  and  the 
pulse  sinks  from  150  to  15  beats  per  minute.*  Thus  the 

*  See  Carpenter. 


HYBERNATION.  145 

functions  of  animal  life  are  never  totally  suspended  during 
winter. 

There  appears  to  be  also  some  continuance  of  vital  ac- 
tivity amongst  plants,  as  for  example,  evergreens.  From 
the  very  nature  of  things  these  plants  must  change  their 
leaves  j  but  they  do  it  in  a  manner  less  rapid  and  visible, 
one  leaf  replacing  the  other  in  such  a  way  that  the  tree  is 
never  totally  defoliated.  In  the  spring  of  the  year  there 
is  a  partial  leaf-fall  from  the  branches  of  evergreens. 
These  plants  therefore  retain  their  capillaries,  which  are 
more  or  less  in  action  through  the  winter  months. 

A  low  degree  of  warmth  will,  even  in  the  depth  of 
winter,  start  the  sap  of  plants.  Thus,  if  incisions  be 
made  into  the  stem  and  branches  of  a  young  maple  in 
winter,  if  the  weather  should  become  mild,  the  sap  wiHr 
be  seen  to  trickle  from  the  wound.  So  also  coniferous 
plants,  which  abound  in  resin,  maintain  their  temperature 
above  the  freezing-point  in  the  severest  weather.  Their 
fluids  are  never  congealed,  owing  to  their  viscidity,  and 
they  can  therefore  resist  the  cold  when  it  destroys  all  the 
vegetable  life  around  them. 

Vegetable  and  animal  life  is  therefore  more  or  less  in 
a  state  of  activity  during  the  winter  months,  although  as 
a  general  thing,  winter  is  a  state  of  repose  to  all  the  lower 
forms  of  organized  nature, — the  nutritive  fluid  slowly  accu- 
mulating in  their  tissues. 

But  the  vernal  sun  once  more  pours  forth  on  the  cold, 
damp  earth,  his  warm,  life-giving  radiance ;  the  earth  and 
atmosphere  are  by  the  force  of  vital  attraction  again  woven 
into  green  leaves  and  beautiful  flowers,  and  the  animal  crea- 
tion issue  forth  from  their  hiding-places  to  partake  of  the 
rich  feast.  This  rapid  development  of  vegetable  and  animal 
life,  together  with  all  its  varied  and  deeply  instructive 
13 


146          REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

phenomena,  what  is  it  but  the  bursting  forth  of  the  pent- 
up  stream  of  vitality  ?  This  display  of  its  strength  is 
commensurate  with  its  former  manifestations  of  feebleness. 
It  is  re-invigorated  nature  awakening  from  repose,  and 
offering  her  tribute  of  thankfulness  to  that  beautiful  star 
the  sun,  during  whose  absence  all  nature  mourns,  at  whose 
coming  all  nature  rejoices,  whose  many-colored  rays  dif- 
fusive of  life  and  beauty  wherever  they  fall,  are  but  pencil- 
ings  from  the  Eternal  for  our  instruction. 

Every  organized  being,  whether  plant  or  animal,  springs 
invariably  from  an  individual  perfectly  similar  to  itself,  to 
which  it  adheres  during  a  space  of  time  more  or  less  long, 
and  from  which  it  is  finally  separated  at  a  definite  period 
under  the  form  of  a  seed,  spore,  or  ovum.  The  seed  and 
ovum,  under  envelopes  more  or  less  resisting,  enclose  a 
germ.  Within  this  germ  all  the,organs  of  the  adult  animal 
and  plant  exist  in  a  rudimentary  condition.  Germination, 
or  the  act  by  which  these  organs  disentangle  themselves 
from  their  envelopes,  does  not  increase  their  number,  but 
only  augments  their  size  and  modifies  their  form. 

The  development  of  the  embryo  within  the  ovum  of  the 
animal  and  plant,  takes  place  in  pretty  much  the  same 
way.  We  have  seen  that  vegetable  fecundation  consists  in 
the  simple  contact  of  the  free  extremity  of  the  pollen  tube 
with  the  embryo  sac  of  the  ovule.  It  is  then  that  the  em- 
bryo develops  in  the  interior  of  the  embryonic  vesicle,  and 
it  is  interesting  to  follow  the  series  of  changes  which  take 
place  in  this  last  organ. 

The  embryonic  vesicle  is  at  first,  simply  a  spherical  cell, 
developed  at  the  end  of  the  suspehsory  filament,,  filled  with 
fluid,  and  containing  granular  matter.  A  little  time  after 
fecundation,  a  longitudinal  septum,  in  the  same  direction  as 
the'suspensor,  is  seen  to  form  across  the  cavity  of  the  cell, 


VEGETABLE  AND  ANIMAL  OVULES  COMPARED.      147 

which  thus  becomes  divided  into  two  cells.  Very  soon 
each  of  these  cells  is  divided  into  two  others,  which  again 
prove  the  same  segmentation ;  the  mass  of  cellular  tissue 
thus  formed,  goes  on  developing,  and  ultimately  organizes 
itself  into  a  seed  which  contains  an  embryo  capable  of  repro- 
ducing the  plant. 

Now  what  relation  subsists  between  the  ovule  of  flower- 
ing plants  and  the  ovule  of  animals  ?  This  is  an  interesting 
question,  deserving  of  some  attention.  In  the  higher  order 
of  animals  the  ovule  exists  in  the  ovarian  mass,  or  in  tubes 
which  supply  its  place  in  animals  of  a  simpler  organization. 
It  appears  at  first  under  the  form  of  a  simple  utricle,  in  the 
inside  walls  of  which  exists  another  much  smaller,  called 
the  germinal  vesicle.  This  last  disappears  after  fecunda- 
tion. It  is  within  the  primitive  utricle  that  the  vitellus 
exists,  a  matter  formed  at  first  of  a  granular  substance, 
which,  by.successive  segmentation,  divides  itself  into  globules 
more  and  more  numerous.  This  body,  the  vitellus,  by 
degrees  organizes  itself  into  a  tissue,  the  basis  and  frame- 
work of  the  germ  or  embryo.  The  animal  ovule  is  there- 
fore represented  in  the  plant  by  the  embryonic  vesicle,  and 
the  granular  matter  which  it  contains  is  analogous  to  the 
vitellus  of  the  egg ;  since  both  are  transformed  by  successive 
segmentations  into  cellular  tissue,  and  finally  into  the  em- 
bryo. The  embryonic  sac  and  the  walls  of  nucleus  are  only 
the  accessory  parts,  analogous  to  the  yolk  of  the  egg  in 
birds ;  that  is  to  say,  they  furnish  to  the  young  embryo  the 
first  materials  of  nutrition,  and  end  by  being  totally  ab- 
sorbed. 

Among  vertebrated  animals  the  development  of  the  em- 
bryo may  be  best  observed  in  the  eggs  of  fishes.  Being 
transparent,  they  do  not  require  to  be  cut  open,  and  by 
sufficient  caution  the  whole  series  of  changes  may  be  ob- 


148  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

served  on  the  same  individual;  whereas,  if  the  eggs  of 
birds  are  employed,  which  are  opaque,  an  egg  must  be 
sacrificed  for  each  observation.* 

The  only  essential  difference  between  the  egg  of  niam- 
mifers,  and  the  human  species  in  particular,  compared  with 
the  eggs  of.  oviparous  animals,  is  in  its  excessive  minute- 
ness. "When  fully  developed,  its  diameter  hardly  amounts 
to  the  tenth  of  a  line.  It  consists  in  a  very  small  vitelline 
mass,  enveloped  in  a  thick  transparent  membrane,  which 
some  authors  have  called  the  chorion,  whilst  others  have 
considered  it  as  representing  the  albuminous  part.  These 
ovules  are  each  placed  in  the  vesicles  of  Graaf,  which  are 
small  bladder-like  bodies,  contained  within  the  ovarium, 
the  remainder  of  the  vesicle  being  filled  with  albuminous 
fluid.  At  the  time  corresponding  to  the  epoch  of  rut  or 
menstruation,  the  Graafian  vesicles  are  ruptured  and  the 
ovule  escapes,  is  immediately  seized  by  the  fimbriated  pro- 
cesses of  the  fallopian  tube,  and  thence  conveyed  along  the 
tube  as  far  as  the  uterus.  If,  in  its  course,  the  egg  encoun- 
ters the  seminal  matter  of  the  male,  fecundation  is  effected. 
It  then  becomes  attached  to  a  point  of  the  matrix,  where  it 
passes  through  all  its  developments  till  the  moment  when 
it  arrives  at  maturity.  It  then  comes  out  to  the  exterior 
and  its  extra-uterine  life  commences.  If,  on  the  contrary, 
the  egg  is  not  fecundated,  it  usually  dies  within  a  few  days, 
and  is  lost  to  reproduction. 

The  seminal  matter  which  fertilizes  the  ovule,  is  in 
animals  ordinarily  a  compact  fluid,  which  contains  granu- 
lations more  or  less  abundant,  and  animated  corpuscles 
called  spermatozoa,  or  spermatic  animalcules  of  a  very 
variable  form.  The  spermatozoa  have  a  body  some- 
times round,  and  occasionally  pyriform  or  cylindrical, 

*  Louis  Agassi/. 


SPERMATOZOA  AND  PHYTOZOA.  149 

terminated  by  a  long  tail.  Sometimes  they  are  spiral  in 
their  outline.  We  observe  them  more  or  less  in  the  male 
semen  of  all  animals. 

The  spermatozoa  are  the  essential  constituents  of  the 
seminal  fluid.  The  fluid  without  them  has  not  in  itself  any 
fertilizing  power.  Sometimes  the  seminal  fluid  is  absent 
altogether,  so  that  they  constitute  the  sole  element  of  the 
semen.  The  fecundation  of  the  ovum  is  therefore  accom- 
plished, by  contact  with  the  spermatozoa  which  swim  in  the 
seminal  fluid.  It  seems  to  be  by  undulations  of  their  tail 
rather  than  by  cilias  that  their  movements  are  effected ;  and 
it  is  obvious  that  they  are  thus  endowed  with  mobility, 
in  order  to  facilitate  their  access  to  the  germinal  vesicle  of 
the  ovum. 

In  all  the  orders  of  Cryptogamous  plants,  bodies  analo- 
gous to  stamens  and  pistils,  termed  antheridia  and  pistil- 
lidia,  have  been  discovered.  The  mutual  action  of  these 
bodies  is  necessary  to  the  development  of  all  the  orders  of 
the  Cryptogamia.  Now  the  cells  of  the  antheridia  of  mosses 
each  contain  a  spiral  filament  which  has  a  globular  head  and 
a  long  tail,  exactly  like  that  of  a  spermatozoa,  and  when 
examined  with  a  power  of  250  diameters,  it  is  seen  to  be  in 
rapid  motion  in  the  cell.  The  spiral  filament  has  therefore 
been  called  a  phytozoon,  and  is  believed  to  exercise  the 
same  function  in  the  vegetable  as  the  spermatozoon  in  the 
animal  economy.  Similar  phytozoa  have  been  detected  in 
the  antheridia  on  the  pro-embryo  of  ferns,  in  that  part  of 
the  fructification  of  Chara,  known  as  the  globule;  in  short, 
in  all  the  organs,  which  represent  the  stamens,  in  Crypto- 
gamous plants. 

The  antheridia  are  globular  in  Chara,  but  they  are  some- 
what ovoid  in  mosses.  They  are  generally  composed  of  a 
mass  of  cells,  variable  in  their  form,  each  containing  a 
13* 


150  REPRODUCTION  IN  PLANTS  AND  ANIMALS. 

movable  phytozoon.  There  is,  therefore,  more  analogy  be- 
tween the  fecundating  matter  of  Cryptogams  and  that  of  ani- 
mals, than  between  the  fecundating  matter  of  Phanerogams 
and  that  of  animals.  The  fine  movable  corpuscles  or  fovilla 
which  may  be  seen  in  the  fertilizing  fluid  matter  which 
descends  the  pollen  tube  to  the  embryo  sac  where  formerly 
thought  to  be  spermatozoa;  but  they  are  only  molecules  of 
starch,  being  colored  blue  by  iodine.  They  are  not  sperma- 
tozoa, as  a  great  many  authors  have  thought. 


. 


PART   IV. 


ON  THE  GEOGRAPHICAL  DISTRIBUTION 
OF  PLANTS  AND  ANIMALS. 


CHAPTER  IX. 

ON  THE  LAWS,  ACCORDING  TO  WHICH,  ANIMALS  AND  PLANTS 
ARE  DISTRIBUTED  ON  THE  SURFACE  OF  THE  GLOBE. 

When  we  examine  the  plants  and  animals  in  different 
parts  of  the  earth,  we  find  that  each  great  country  on  the 
globe  has  its  own  flora  and  fauna.  This  diversity  in  their 
vegetable  productions  is  one  of  the  causes  of  that  particular 
physiognomy  which  landscapes  present  in  the  different  parts 
of  the  earth.  Thus  the  vegetation  which  covers  the  coun- 
tries to  the  north,  consisting  of  immense  forests  of  pine,  fir, 
and  birch,  is  very  different  from  that  of  the  more  temperate 
climates,  where  the  forests  are  less  abundant,  and  possess 
more  of  variety  in  the  species  which  compose  them ;  and 
the  plants  of  the  temperate  zone  are  not  the  same  as  that 
of  tropical  countries,  where  the  climacteric  conditions  are 
favorable  to  the  support  and  development  of  a  continuous 
vegetation  which  is  never  arrested. 

The  geographical  distribution  of  animals  is  intimately 
associated  with  that  of  plants;  for  herbivorous  animals 
can  exist  only  where  there  is  an  adequate  supply  of 
vegetables  suitable  for  their  food;  and  the  carnivorous 
prey  upon  the  herbivorous  races.  Hence  it  is  that  the  fauna 
of  the  different  parts  of  the  earth  presents  the  same  ever- 
varying  aspect  as  its  flora.  The  animals  of  Oregon  and 
California,  for  example,  are  not  the  same  as  those  of  New 
England;  and  in  like  manner  the  animals  of  temperate 
Asia  differ  from  those  of  Europe  and  the  torrid  regions  of 
Africa.  Under  the  torrid  zone,  the  animal  as  well  as  the 


154  THE  GEOGRAPHICAL  DISTRIBUTION 

vegetable  kingdom,  attains  its  highest  development,  whilst 
about  the  poles  it  manifests  the  same  organic  inferiority. 

If  we  begin  to  reflect  on  the  probable  causes  which  have 
produced  this  diversity  of  vegetation  and  animality  in  the 
different  parts  of  the  world,  we  shall  soon  perceive  that  the 
whole  may  be  referred  to  a  few  general  laws.  This  part 
of  the  sciences  of  Zoology  and  Botany,  however,  demands 
new  researches.  The  nature  and  number  of  the  animals 
and  plants  in  all  parts  of  the  world  is  not  yet  known  •  and 
it  is  only  this  particular  knowledge  of  the  plants  and  ani- 
mals of  each  country,  joined  to  numerous  and  exact  geo- 
graphical and  meteorological  observations,  which  will  guide 
us  to  a  correct  knowledge  of  those  general  laws  which  re- 
gulate the  distribution  of  the  plants  and  animals  on  the 
earth's  surface. 

This  branch  of  Natural  History  is  of  very  recent  origin, 
and  owes  its  existence  to  the  philosophical  researches  of 
Humboldt,  Decandolle,  Robert  Brown,  Schow,  Mirbel,  and 
other  eminent  naturalists  of  the  present  century.  Through 
their  labors,  considerable  progress  has  been  made  in  this 
interesting  department  of  the  natural  sciences. 

Some  plants  appear  to  be  capable  of  adapting  themselves 
to  almost  any  climate.  Thus  many  ferns  and  mosses  are 
common  to  both  Europe  and  America,  and  numerous  Eu- 
ropean weeds  infest  the  fields  and  woods  throughout  the 
United  States,  to  the  exclusion  in  some  instances,  even  of  the 
native  denizens  of  the  soil.  So  the  spores  of  Cryptogamous 
plants  are  so  light  that  they  are  easily  borne  on  atmospheric 
currents  across  mountains  and  oceans,  and  this  accounts  for 
the  wide  spread  of  the  same  genera  and  species  over  the 
European  and  American  continents;  but  the  European 
weeds  which  everywhere  present  themselves  to  the  eye  in 
America,  are  certainly  the  result  of  commercial  intercourse 


OF  PLANTS  AND  ANIMALS.  155 

between  the  two  countries,  as  there  is  nothing  in  their 
organization  to  convey  them  in  such  abundance  to  such  vast 
distances  from  their  native  localities. 

Some  species  of  animals  have  also  a  very  extensive 
geographical  range.  The  muskrat  is  found  from  the  mouth 
of  Mackenzie's  river  to  Florida.  The  field-mouse  has 
an  equal  range  in  Europe.  Commerce  has  mingled  to- 
gether the  animals  as  well  as  the  plants  of  the  old  and  new 
worlds.  The  horse,  originally  from  Asia,  was  introduced 
into  America  by  the  Spaniards,  where  it  was  allowed  to 
run  wild,  and  has  thrived  so  well,  that  immense  herds  are 
now  found  scattered  over  the  pampas  of  South  America  and 
the  prairies  of  the  West ;  and  in  the  same  manner  the  do- 
mestic ox  has  become  wild  in  South  America.  Many  ani- 
mals, such  as  the  dog,  the  different  kinds  of  poultry,  and 
several  singing  birds,  seem  to  be  capable  of  living  in  almost 
any  climate,  and  are  fostered  and  encouraged  to  associate 
with  man  on  account  of  the  pleasure  and  service  which  they 
afford  him.  Many  less  welcome  animals  have  also  followed 
him,  as  for  instance,  the  rat  and  the  mouse,  as  well  as  a 
multitude  of  insects,  such  as  the  house-fly,  the  cockroach, 
and  those  which  live  on  the  vegetables  which  he  cultivates, 
as  the  white  butterfly,  the  Hessian-fly,  &c. 

The  generality  of  animals  and  plants  are  not,  however, 
so  flexible  in  their  constitutions.  No  animal,  excepting 
man,  inhabits  every  part  of  the  earth.  Each  great  geogra- 
phical and.  climatal  region  is  occupied  by  some  species  not 
found  elsewhere;  and  each  animal  flourishes  best  within 
certain  limits  beyond  which  it  does  not  range.  It  is  the 
same  with  plants.  Comparatively  speaking,  vegetable 
cosmopolites  are  few  in  number.  The  greater  number  of 
plants  are  very  exacting  as  to  the  conditions  of  their  de- 
velopment, and  will  only  put  forth  foliage,  flowers,  and 


156  THE  GEOGRAPHICAL  DISTRIBUTION 

fruit,  in  a  certain  soil  and,  under  certain  definite  conditions 
of  heat,  light,  and  moisture.  In  this  respect  the  animal 
and  vegetable  world  are  governed  by  the  same  laws. 

Soil  exercises  a  marked  influence  on  the  geographical 
distribution  of  species.  It  is  impossible  to  examine  the 
flora  or  fauna  of  any  country  without  arriving  at  this  con- 
clusion. The  mountains  and  the  valleys,  the  margin  of 
rivers  and  the  shores  of  the  ocean  have  all  their  appro- 
priate vegetable  and  animal  forms.  When  we  burn  a 
plant,  the  materials  attracted  from  the  earth  and  atmo- 
sphere and  blended  together  in  its  organism  are  separated, 
and  we  restore  to  the  atmosphere  the  gaseous  part  of 
the  plant  which  was  taken  from  it,  isolating  the  mine- 
ral matter  derived  from  the  soil  under  the  form  of 
the  incombustible  ash  which  remains.  Now  the  small 
amount  of  ash  left,  proves  that  the  atmosphere  is  the  chief 
source  of  vegetable  nutrition ;  yet  nevertheless  its  import- 
ance is  not  on  this  account  to  be  underrated.  This  ash 
does  not  enter  the  organism  of  the  plant  mechanically 
along  with  the  fluid  matters  absorbed  by  the  roots  from 
the  soil,  for  analysis  has  proved  that  its  chemical  composi- 
sition  varies  in  different  plants.  Therefore,  each  nucleus 
of  cells  which  forms  the  substance  of  the  germinating  seed, 
must  exercise  a  special  attraction  on  certain  inorganic  ele- 
ments, which  it  separates  from  the  other  mineral  matters,  in 
the  midst  of  which  it  grows,  and  which  inorganic  elements 
are  absolutely  necessary  to  the  healthy  evolution  of  the 
embryo  which  it  encloses.  Plants  are  therefore  unques- 
tionably influenced  in  their  localization,  by  certain  peculiar 
inorganic  elements  which  they  derive  from  the  soils  in 
which  they  grow. 

When  the  soil  is  of  such  a  nature  as  to  favor  the  growth 
of  one  particular  species  more  than  another,  it  becomes 


OF  PLANTS  AND  ANIMALS.  157 

covered  exclusively  "by  that  species,  of  which  the  individuals 
form  a  true  society  and  give  a  peculiar  aspect  to  that  re- 
gion. This  congregating  together  of  numerous  individuals 
of  the  same  species,  constituting  what  Humboldt  calls  social 
plants,  always  indicates  great  uniformity  in  the  nature  of 
the  soil.  It  is  thus  that  the  Sphagnum,  or  bog-moss, 
covers  the  soil  to  a  considerable  extent  in  humid  and  ex- 
posed parts  of  forests ;  that  sedges,  heaths,  rhododendrons, 
and  firs,  occupy  immense  spaces  on  the  surface  of  the  earth, 
to  the  exclusion  of  all  other  species,  which  find  themselves 
smothered  out  by  the  social  plants,  these  regions  being 
their  especial  domain. 

The  knowledge  of  the  choice  or  predilection  of  a  species 
for  this  or  that  situation,  is  current  amongst  all  engaged 
in  practical  horticulture,  and  is  called  into  requisition 
every  day,  in  the  formation  of  groups  and  beds  of  flowers 
in  parks  and  gardens. 

It  is  well  known  that  many  animals  are  equally  social 
in  their  habits.  Birds  migrate  in  flocks;  sheep  congre- 
gate in  pastures;  and  the  prairies  of  the  far  West  are 
sometimes  covered  with  herds  of  buffaloes. 

Temperature. — If  the  earth  were  throughout  homoge- 
neous, if  its  surface  were  not  formed  of  land  and  sea,  of 
islands  and  continents,  of  mountains  and  plains,  the  tem- 
perature of  a  determinate  point  of  the  globe  would  be 
given  by  its  latitude,  and  the  isothermal  lines,  or  lines  of 
equal  temperature,  would  be  parallel  to  themselves  and  to 
the  equator.  But  the  surface  of  the  earth  is  not  homo- 
geneous. Elevation  has  the  same  effect  on  temperature  as 
an  increase  of  distance  from  the  equator,  even  under  the 
same  parallels  of  latitude.  Now  in  proportion  as  countries 
are  elevated,  in  the  same  ratio  is  their  temperature  reduced. 
This  remark  applies  not  only  to  those  mountain  chains 
14 


158  THE  GEOGRAPHICAL  DISTRIBUTION 

whose  snowy  peaks  are  seen,  even  in  tropical  countries, 
but  also  to  those  plateaus  or  elevated  table-lands,  which 
abound  in  different  parts  of  the  world.  The  water  with 
which  a  vast  portion  of  the  earth's  surface  is  overspread 
greatly  modifies  its  temperature.  Countries  situated  in 
the  neighborhood  of  the  ocean,  are  always  cooler  than 
those  which  are  removed  from  its  influence.  The  iso- 
thermal lines  are  not  therefore  parallel  to  the  equator, 
excepting  in  the  neighborhood  of  the  equinoctial  line,  but 
form  an  irregular  curve  around  the  earth's  surface.  Tem- 
perature undoubtedly  influences  the  geographical  distribu- 
tion of  plants.  To  every  species  of  plant  there  is  a  certain 
degree  of  temperature  necessary  before  it  will  germinate. 
Hence  it  is  that  every  month  produces  its  own  flora,  the 
result  of  the  ever-varying  temperature  of  the  year,  and 
each  zone  produces  its  own  vegetation  which  would  not 
flourish  elsewhere. 

Light. — The  influence  of  light  on  vegetation  is  perhaps 
not  so  great  as  that  of  temperature,  yet  it  is  nevertheless 
deserving  of  an  especial  notice.  The  decomposition  and 
consolidation  of  the  elementary  food  of  plants,  the  forma- 
tion of  the  green  parts,  the  exhalation  of  moisture  by 
their  leaves,  its  absorption  by  their  roots,  and  all  the  other 
circumstances  of  vegetable  life,  are  owing  to  the  illumi- 
nating power  of  the  sun.  In  tropical  countries,  where  the 
light  of  the  sun  is  the  most  powerful,  we  meet  with  plants 
which  have  the  most  intense  colors,  the  strongest  odors, 
and  the  most  active  properties.  These  plants  when  culti- 
vated in  the  stove,  never  acquire  the  fragrance  and  virtues 
which  they  possessed  in  their  native  country ;  for  although 
we  can  place  them  in  an  atmosphere  of  the  same  tempera- 
ture as  their  own  in  these  northern  climates  by  applying 


OP  PLANTS  AND  ANIMALS.  159 

artificial  heat,  yet  it  is  impossible  to  .replace  the  splendor 
of  the  southern  sun. 

In  tropical  countries,  the  rays  of  the  sun  fall  perpendi- 
cularly, and  therefore  his  light  is  much  more  intense 
there  than  in  the  temperate  or  polar  regions.  As  we  pass 
from  the  equator  to  the  poles,  the  incidence  of  the  rays 
becomes  more  oblique,  and  consequently,  their  brightness 
and  stimulating  power  on  the  vegetable  and  animal  creation 
must  be  diminished  in  the  same  ratio. 

All  the  effects  of  light  on  vegetation  are  not  yet  fully 
understood.  In  temperate  climates,  in  early  spring,  the 
temperature  depends  in  a  great  measure  on  the  prevailing 
currents  of  air.  If  these  currents  come  to  us  from  the 
north,  although  the  sky  is  cloudless  and  the  vernal  sun 
smiles  cheerfully  once  more  on  the  leafless  forests  and  the 
flowerless  fields,  yet  the  cold  will  prevent  the  development 
of  vegetable  life.  But  are  the  plants  wholly  uninfluenced 
by  the  light  in  such  circumstances  ?  It  seems  possible 
that,  independently  of  the  heat,  the  constantly  increasing 
light  may  have  a  somewhat  stimulating  effect  on  vegeta- 
tion. We  are  not  aware  of  any  facts  which  confirm  this 
suggestion,  but  the  subject  is  deserving  of  attention. 

It  is  well  known  that  plants  grown  in  a  window  turn 
their  leaves  to  the  light,  and  that  the  pots  in  which  they 
are  kept  require  to  be  turned  occasionally  in  order  to  pre- 
vent them  from  growing  all  on  one  side.  The  daisy  and 
dandelion  are  supported  on  a  long  stalk,  if  their  flowers 
grow  in  rank  grass ;  and  become  sessile  on  a  shaven  lawn, 
or  in  spots  to  which  the  light  has  free  access.  Light  also 
influences  the  position  of  leaves  on  the  stem,  which  are 
always  arranged  so  as  to  be  most  favorably  situated  for  its 
reception.  The  opposite  leaves  of  labiate  plants  which 
usually  cross  each  other  at  right-angles,  develop  in  the 


160  THE  GEOGRAPHICAL  DISTRIBUTION 

same  plane,  when  the  stem  becomes  horizontal  or  its 
branches  take  a  drooping  growth.  This  change  of  position 
may  be  observed  especially  in  the  ground-ivy  (Glechorna 
hederacea.)  The  direction  of  the  branches  of  trees  is 
also  greatly  influenced  by  the  light.  Thus  the  lower 
branches  are  more  horizontal  and  stretch  further  from  the 
stem  than  those  towards  the  summit  of  the  tree. 

Humidity. — Vegetation  is  greatly  promoted  by  a  moist 
condition  of  the  atmosphere.  Water  is  as  necessary  in 
germination,  as  in  all  the  other  phenomena  of  vegetable 
life.  It  penetrates  into  the  substance  of  the  seed,  softens 
its  envelopes,  and  makes  the  embryo  swell.  It  therefore 
places  the  seed  in  the  conditions  which  are  the  most  favor- 
able for  germination. 

The  quantity  of  rain  which  falls,  varies  greatly  in  dif- 
ferent parts  of  the  world.  There  are  enormous  tracts  of 
land  on  which  rain  never  falls.  In  some  places  it  rains 
almost  perpetually.  Between  the  tropics,  the  rains  follow 
the  sun ;  when  he  is  north  of  the  equator,  the  rains  prevail 
in  the  northern  tropics,  and  when  he  is  south  of  that  line, 
in  the  southern  tropics ;  hence  one  half  of  the  year  is  ex- 
tremely wet,  and  the  other  half  very  dry.  The  changes 
take  place  at  the  equinoxes,  when  the  sun  crosses  the  line. 
In  the  temperate  zone  rain  falls  at  all  seasons,  though 
more  abundantly  in  some,  than  in  others.  This  unequal  dis- 
tribution of  heat,  light,  and  rain,  over  the  earth's  surface, 
must  necessarily  produce  a  great  difference  in  vegetation. 

If  we  would  however  approximate  to  more  correct 
and  philosophical  views  respecting  the  influences  of  these 
grand  stimulants  of  vegetation  and  animality,  it  is  neces- 
sary to  consider  their  influence,  not  so  much  separately,  as 
in  a  state  of  combination,  and  its  effect  in  different  parts 
of  the  earth. 


OF  PLANTS  AND  ANIMALS.  161 

Tropical  countries  may  be  truly  regarded  as  the  paradise 
of  trees  and  flowers.  The  intense  heat  and  light  of  the  sun 
combined  with  the  humidity  of  the  atmosphere,  cause  the 
rapid  development  of  a  rich  and  varied  flora.  There  are 
no  wintry  winds,  falling  snows,  or  hard  frosts,  to  blight  the 
magnificent  vegetable  beauty  with  which  these  regions  are 
overspread.  The  forests  of  the  tropics,  instead  of  being 
composed,  as  in  temperate  climates,  of  a  small  number  of 
trees  with  desiduous  leaves,  presenting  the  same  wearisome, 
monotonous  aspect,  exhibit  a  much  .greater  variety  of  arbor- 
escent forms,  which,  clothed  with  perpetual  verdure,  are 
covered  throughout  the  year  with  fruits  and  flowers  in  dif- 
ferent stages  of  growth.  The  grasses  are  there  ligneous  and 
gigantic,  some  of  them  equal  in  height  to  the  trees  of  tem- 
perate climates;  immense  woody' vines  of  fantastic  and 
ever  varied  form,  elevate  themselves  to  the  summit  of  the 
tallest  trees,  with  the  leaves  and  blossom  of  which  their 
foliage  and  flowers  are  often  beautifully  intermingled. 
The  tall  and  elegant  palms  and  tree  ferns,  with  their  mag- 
nificent bouquet  of  gigantic  and  pendulous  fronds  towering 
above  the  rest  of  the  trees  of  the  forest,  are  seen  afar  off  on 
the  ocean,  and  are  the  first  objects  which  present  themselves 
as  the  traveller  approaches  the  shores  of  tropical  countries. 

The  development  of  animality  is  equally  luxuriant.  All 
the  principal  types  of  animal  life  are  represented  on  the  most 
magnificent  scale.  An  astonishing  variety  of  birds  with  the 
most  brilliant  plumage,  make  the  forests  vocal  with  their 
melody.  We  need  only  refer  to  the  tribe  of  humming  birds 
which  numbers  no  less  than  300  species.  Here  reside  the 
noble  lion,  the  beautiful  though  ferocious  tiger,  the  largest 
of  the  cat  tribe.  This  is  the  home  of  the  great  pachy- 
dermata,  the  elephant,  the  hippopotamus,  and  the  tapir. 
The  reptilia  assume  their  largest  forms.  Immense  croco- 

14* 


162  THE  GEOGRAPHICAL  DISTRIBUTION 

diles,  tortoises,  and  serpents  frequent  the  rivers,  marshes, 
and  moist  woods.  The  seas  teem  with  crustaceans  and 
every  order  of  molluscous  animals.  The  shores  are  covered 
with  their  shells,  which,  in  these  sunny  regions,  acquire  the 
most  rich  and  variegated  hues.  The  insects  are  as  brilliant 
as  they  are  numerous.  There  can  be  no  doubt  whatever 
that  all  the  rich  coloring  which  is  spread  over  aniniality  as 
well  as  vegetation  in  tropical  countries,  is  to  be  attributed  to 
the  brightness  of  the  sun's  rays.  Tropical  birds,  for  ex- 
ample, reared  under  an  artificial  temperature  in  cold  coun- 
tries, never  acquire  that  brilliancy  of  plumage  which  dis- 
tinguishes them  in  their  native  haunts. 

As  we  pass  from  tropical  into  temperate  climates,  the 
heat  decreases,  the  rays  of  the  sun  become  more  oblique, 
and  consequently  less  vivid ;  in  a  word,  all  the  exciting- 
causes  of  vegetation  gradually  diminish  in  intensity.  The 
tall  and  graceful  palm  tree,  the  plantain  and  the  banana, 
the  cotton-tree  and  the  sugar-cane  are  no  longer  visible. 
Vegetation  is  despoiled  of  its  magnificence  and  variety,  and 
takes  a  humbler  and  simpler  form.  Accordingly  we  find 
that  plants  with  ligneous  and  persistent  stems  are  fewer  in 
number,  and  that  there  is  a  greater  predominance  of  such 
as  are  herbaceous,  and  which  therefore  perish  annually. 
*  Plants  with  herbaceous  stems  have  precisely  the  same 
growth,  as  far  as  it  goes,  as  those  which  are  ligneous  and 
persistent.  Any  one  can  speedily  convince  himself  of  this. 
There  is  visible  on  the  cross  section  the  same  concentrical 
disposition  of  the  matter  of  the  stem  into  pith,  wood  and 
bark,  and  the  same  development  of  branches  in  the  axils  of 
the  leaves.  But  the  heat  is  not  spread  through  a  sufficient 
number  of  months,  and  the  period  is  too  short  for  the  plant 
to  run  through  all  the  phases  of  its  development.  The  whole 
process  is  therefore  stopped  in  its  first  stages,  and  the  stem 


OP  PLANTS  AND  ANIMALS.  163 

with  its  branches  and  flowers,  dies  down  to  the  ground,  and 
disappears  from  the  earth's  surface  on  the  approach  of  winter. 
In  other  instances,  where  woody  matter  is  deposited  in 
greater  abundance,  the  leaves  and  flowers  perish,  but  life 
remains  passive  in  the  stem.  The  cold  has  arrested  the 
vegetable  machinery  but  produces  no  disarrangement  of  its 
parts,  on  the  contrary,  a  section  of  the  autumnal  bud, 
shows  beautifully  the  young  embryo  leaves  and  the  un- 
developed internodes  [of  the  next  year's  growth,  already 
formed  in  them,  and  but  awaiting  the  return  of  the  warmth 
and  brightness  of  the  sun,  to  come  forth  out  of  this  their 
hybernaculum,  and  again  exhibit  the  same  vital  movements. 

The  seed  and  ovum  in  vegetables  and  in  the  lower  forms 
of  animals,  is  but  a  retreat  into  which  exhausted  vitality 
retires  for  a  season  in  order  to  recover  its  wonted  energies; 
it  also  affords  a  shelter  for  the  young  embryo  during  the 
prevalence  of  those  conditions  which  are  unfavorable  for  its 
development.  Accordingly,  we  find  that  the  seeds  of  many 
early  flowering  annuals  germinate  again  in  autumn,  as  the 
light  and  heat  of  the  sun  are  then  much  the  same  as  in 
early  spring.  A  little  family  of  plants  is  thus  seen  rising 
around  their  aged  and  dying  parent.  In  some  instances, 
the  individuals  of  this  family  arrive  again  at  an  adult  state, 
and  flowers  as  well  as  leaves  appear;  generally,  however, 
the  germinating  seeds  can  only  produce  leaves,  the  ap- 
proach of  cold  weather  arresting  all  further  development. 
These  and  many  other  appearances  in  nature  are  deserving 
of  a  greater  share  of  attention  than  has  hitherto  been  allot- 
ted to  them.  All  practical  gardeners  and  botanists  are 
acquainted  with  many  plants  which  flower  in  spring,  and 
again  develop  in  autumn,  on  a  return  of  similar  conditions 
of  light,  temperature,  and  moisture. 

That  the  vegetable  machinery  would  continue  in  motion 


164  THE  GEOGRAPHICAL  DISTRIBUTION. 

and  simply  stops  in  consequence  of  the  decreasing  heat  and 
light  of  the  sun,  is  evident  from  the  fact,  that  plants  which 
are  annual  and  herbaceous  in  temperate  climates,  be- 
come ligneous  perennials  in  the  tropics.  The  castor  oil 
plant,  (Ricinus  cornmunis,)  for  example,  in  Pennsylvania, 
puts  forth  large  peltate-palmate  leaves,  and  grows  from 
three  to  eight  feet  in  height,  but  is  destroyed  by  the  first 
frosts  of  autumn.  In  the  happy  regions  within  the  tropics, 
its  stem  is  ligneous  and  persistent,  and  it  grows  into  a 
powerful  and  lofty  tree.  It  is  the  same  with  the  Euphor- 
biacese,  Labiatae,  Leguminosae,  Boraginaceas,  Hypericacese, 
Rubiaceae,  YerbenaceaD,  Polygonaceae,  Composite,  and  a 
host  of  other  plants  which  we  tread  under  our  feet  in 
Pennsylvania ;  these  die  down  to  the  earth's  surface  and  dis- 
appear from  the  landscape  on  the  approach  of  winter,  which 
arrests  the  movements  of  life  in  all  the  lower  forms  of  organ- 
ization in  temperate  climates.  In  the  tropics,  these  very 
plants,  so  herbaceous  and  perishable  with  us,  take  a  lig- 
neous and  persistent  form,  and  elevate  themselves  majes- 
tically into  the  air.  Excepting  on  the  mountain  summit, 
snow  never  falls  on  any  other  part  of  the  warm  and  sunny 
landscape,  and  the  traveller  wanders  amid  the  arborescent 
forms  of  Legurninosse,  Euphorbiaceae,  Labiatae,  and  Bora- 
ginaceae ;  or  if  he  be  in  the  island  of  St.  Helena,  reposes 
beneath  the  shade  of  forests  of  Solidago,  Sonchus,  and 
Echium.  The  herbaceous  and  perishable  annual  has  be- 
come transformed  into  the  ligneous  and  enduring  perennial. 
The  plant  whose  humble  growth  and  delicate  beauty  drew 
our  admiration  as  it  grew  at  the  foot  of  some  tall  oak  or 
lofty  buttonwood,  is  now  itself  one  of  the  noblest  trees  of 
the  forest.  Development  has  gone  on,  and  we  see  the 
result  of  the  magic  influence  of  a  continuity  of  warmth  and 


OP  PLANTS  AND  ANIMALS.  165 

brightness  in  the  majestic  form  which  now  stands  before 
our  eyes. 

The  fauna  of  temperate  climates,  like  its  flora,  presents 
the  same  picture  of  arrested  development  and  temporary 
suspension  of  the  powers  of  life  during  the  winter  months. 
We  have  a  considerable  number  of  animals  of  graceful 
form,  animated  appearance,  and  varied  colors,  though  they 
are  less  brilliant  than  those  found  in  tropical  regions. 
There  is  a  greater  uniformity  amongst  them.  Notwith- 
standing the  immense  extent  of  country,  the  same  families, 
and  frequently  the  same  genera,  are  found  in  countries 
widely  apart  from  each  other.  There  are  even  a  few  ter- 
restrial species,  regarded  as"  identical  in  the  temperate 
regions  of  America  and  Europe ;  but  their  supposed  num- 
ber is  constantly  diminished  as  more  accurate  observations 
are  made.  The  reptilia  are  much  reduced  in  size;  the 
lizard  and  viper  take  the  place  of  the  gigantic  crocodile  and 
boa  constrictor.  The  tortoises  are  small  and  of  medium 
size.  All  classes  of  molluscs  are  represented;  but  their 
shell,  are  deprived  of  much  of  that  beauty  which  charac- 
terizes the  shells  of  warmer  climates.  The  patient  camel 
and  dromedary,  the  half-reasoning  elephant,  the  beautiful 
zebra  and  tiger,  are  replaced  in  temperate  climates  by  the 
horse  and  ass,  the  dog,  wolf,  and  wild  cat. 

All  animals  which  store  up  provisions,  such  as  the 
squirrel,  the  marmot,  the  beaver,  and  the  bee,  are  peculiar 
to  the  temperate  regions  of  the  earth.  It  is  obvious  that 
such  instincts  would  be  out  of  place  in  tropical  countries, 
where  vegetation  presents  herbivorous  animals  and  insects 
with  an  abundant  supply  of  food  at  all  times. 

On  the  approach  of  cold  weather  the  trees,  with  the 
exception  of  the  pine,  fir,  and  other  coniferse,  drop  their 
leaves ;  the  insects  retire,  and  the  animals  wnich  live  on 


166  THE  GEOGRAPHICAL  DISTRIBUTION 

them,  either  migrate  to  other  countries,  or  pass  the  winter 
in  a  state  of  torpor,  from  which  they  awake  in  spring. 
This  is  especially  the  case  with  the  birds,  which  are  all 
migratory  in  their  habits.  The  most  beautiful  species  come 
to  us  from  the  sunny  south,  and  disappear  on  the  approach 
of  winter. 

In  proportion  as  we  approach  the  polar  regions,  the 
trees  become  stunted  and  dwarfed  in  their  growth,  the 
number  of  genera  and  ^species  is  still  further  diminished, 
the  oak,  the  walnut,  the  chestnut,  and  the  hickory,  are 
replaced  by  dark  and  sombre  forests  of  coniferous  plants, 
amongst  which  pines  and  firs  are  the  most  prominent. 
Finally,  these  plants  gradually  disappear,  and  the  last 
lingering  remnants  of  vegetable  life  are  seen  in  the  form  of 
mosses,  lichens,  and  other  cryptogamous  plants,  the  exces- 
sive rigors  of  the  climate  preventing  any  higher  indications 
of  vegetable  life. 

The  animals  in  the  arctic  regions  are  few  in  number, 
and  their  tints  as  dusky  as  the  northern  heavens.  There 
is  not  a  single  bird  with  brilliant  plumage,  and  not  a  fish 
with  various  hues.  The  artic  regions  form  a  district  com- 
mon to  Europe,  Asia,  and  America.  On  this  account  the 
animals  inhabiting  them  are  sometimes  identical ;  in  fact, 
there  is  no  genus  of  quadrupeds  in  the  Arctic  regions 
which  is  not  common  to  the  three  continents.  The  most 
conspicuous  animals  are,  the  reindeer,  the  white  bear,  the 
polar  hare,  the  white  fox,  lemming,  and  various  seals. 
There  are  immense  flocks  of  predaceous  and  aquatic  birds, 
gulls,  cormorants,  ducks  and  geese,  all  belonging  to  the 
lowest  orders.  Reptiles  are  altogether  wanting.  The  articu- 
lata  are  represented  by  numerous  marine  worms  and  minute 
crustaceans.  Insects  are  rare  and  of  inferior  types.  Mol- 
lusca  are  sparsely  scattered  m  the  adjacent  seas  along  with 


OF  PLANTS  AND  ANIMALS.  167 

a  few  star  fishes  and  echini.  We  must  not  omit  the 
whales,  which  are,  however,  the  lowest  of  all  the  mammalia. 
This  assemblage  of  animals  is  decidedly  inferior  to  the 
temperate  and  tropical  faunas. 

We  have  already  intimated  that  "elevation  has  the 
same  effect  on  temperature  as  an  increase  of  distance  from 
^the  equator."  Hence  there  is  a  remarkable  similarity  be- 
tween the  plants  and  animals  which  cover  a  hemisphere 
from  the  equator  to  the  poles,  and  those  which  clothe  the 
sides  of  a  tropical  mountain,  from  its  warm  and  sunny  base 
to  its  cold  and  snowy  summit.  The  species,  genera,  and 
even  the  'families  of  both  plants  and  animals  growing  in 
the  country  surrounding  its  base,  may  be  entirely  different 
from  the  vegetable  productions  of  Europe.  But  here,  ele- 
vation above  the  ocean  level,  acts  in  the  same  manner  on 
vegetation  as  an  increase  of  distance  from  the  equator.  In 
proportion  as  we  ascend  the  mountain,  the  fauna  and  flora 
gradually  lose  their  tropical  character,  and  assume  the  ap- 
pearance of  that  without  the  tropics ;  the  climate  becomes 
cooler,  until  at  length  the  tropical  plants  disappear,  and 
European  genera,  and  even  species  analogous  if  not  abso- 
lutely identical  with  those  of  the  temperate  climates  of 
Europe,  present  themselves  to  the  eye  of  the  astonished 
observer.  As  we  approach  the  limits  of  pe>|>etual  snow, 
the  vegetation  becomes  wholly  cryptogamous,  and  similar 
to  that  of  the  arctic  regions. 

M.  Mirbel  has  therefore  very  properly  compared  the 
terrestrial  globe  to  two  immense  mountains,  whose  bases 
are  united  at  the  equator,  and  whose  summits  are  the 
arctic  regions  around  its  northern  and  southern  poles. 

. 
. 


168  THE  GEOLOGICAL  SUCCESSION 


CHAPTER  X. 

ON  THE  GEOLOGICAL  SUCCESSION  OF  PLANTS  AND  ANIMALS, 
OR  THEIR  DISTRIBUTION  IN  TIME. 

In  the  preceding  chapters  we  have  endeavored  to  show 
that  the  operations  of  organic  law  are  the  same  in  plants 
and  animals.  In  order  to  render  the  argument  complete, 
it  is  necessary  to  consider  them  in  the  order  of  their  ap- 
pearance on  the  earth's  surface ;  and  for  this  purpose  we 
must  examine  their  fossil  remains  and  their  position  in  the 
rocks.  The  study  of  these  remains  constitutes  the  science 
of  Paleontology — one  of  the  most  essential  branches  of 
Botany  and  Zoology. 

By  this  science  we  are  taught  that  the  present  arrange- 
ments of  land  and  water,  and  the  forms  of  animal  and  vege- 
table life  on  the  earth's  surface,  are  the  result  of  a  long 
succession  of  antecedent  changes  of  which  the  earth's  crust 
has  preserved  the  memorial.  The  History  of  the  Earth  has 
been  written  in  its  strata,  which  have  been  very  properly 
termed  "  the  leaves  of  the  stone  book."  But  the  language 
left  on  these  stony  pages  can  only  be  interpreted  by  a  care- 
ful and  accurate  knowledge  of  the  living  creation,  and  of  the 
laws  which  now  govern  the  distribution  and  development 
of  species.  Natural  History  is  the  alphabet  of  geology. 
The  highest  attainments  in  the  natural  sciences  are  re- 
quired for  these  researches. 

The  knowledge  of  Botany  which  is  required  to  throw 
light  on  fossil  plants,  must  be  both  varied  and  extensive.  It 
is  obvious  that  the  Linnaean  system  is  of  no  use  in  deter- 


OF  PLANTS  AND  ANIMALS.  169 

mining  genera  and  species,  because  it  is  founded  on  charac- 
ters which  have  not  been  preserved,  viz.,  the  different  parts 
of  the  flower.  Fossil  plants  are  not  so  easily  determined 
as  recent  species,  because  their  parts  are  usually  separated 
from  each  other.  It  is  very  seldom  that  any  traces  of  their 
reproductive  organs  are  left.  Fragments  of  stems,  leaves, 
and  occasionally  seeds,  are  the  only  data  by  which  the  plant 
can  be  determined.  We  have  to  fall  back,  therefore,  on 
our  knowledge  of  the  natural  system.  There  must  be  a 
thorough  acquaintance  with  the  different  natural  orders, 
and  a  familiarity  with  vegetable  anatomy.  There  must 
be  a  competent  knowledge  of  the  minute  structure  of  all 
the  organs  of  plants,  such  as  their  root,  stem,  leaves,  bark, 
and  fruit,  and  of  the  markings  which  they  exhibit  on  their 
exterior  surface,  together  with  some  general  ideas  of  the 
vegetation  of  tropical  climates  as  well  as  of  cooler  latitudes, 
before  the  living  affinities  of  the  fossil  plant  can  be  deter- 
mined. 

As  fossil  plants  are  generally  found  in  detached  frag- 
ments, it  is  necessary  to  reconstruct  the  plant  as  completely 
as  possible,  and  to  determine  the  relations  of  its  several 
portions  to  each  other.  It  is  evident  that  this  must  be  a  very 
difficult  task -,  but  it  is  a  very  necessary  one,  for  the  neglect 
of  it  has  led  to  a  needless  multiplication  of  fossil  species, 
portions  of  the  same  plant  having  been  described  as  sepa- 
rate species  or  genera. 

A  knowledge  of  Comparative  Anatomy  is  also  necessary. 
To  a  person  unacquainted  with  this  science  it  may  appear 
impossible,  that  from  a  single  fragment  of  a  fossil  bone  or 
tooth,  Naturalists  are  able  to  determine  the  general  character 
of  its  skeleton,  and  from  thence  to  infer  its  appearance  and 
mode  of  life.  Yet  all  this  is  true.  If  we  find,  for  example, 
a  single  fossil  tooth,  if  it  be  a  molar,  it  is  sufficient  to  indi- 
15 


170  THE  GEOLOGICAL  SUCCESSION 

cate  the  mode  of  life  of  the  animal  to  which  it  belonged, 
and  to  show  that  it  fed  on  vegetables,  as  the  other  organs 
of  the  body  constantly  correspond  in  structural  adaptation 
to  the  same  function.  There  is  the  utmost  harmony  and 
adaptation  of  parts  to  each  other  amongst  the  several  bones 
of  the  skeleton,  and  hence  each,  taken  by  itself,  indicates 
and  gives  form,  to  all  the  others.  This  has  been  shown  by 
the  acute  and  laborious  researches  of  Cuvier  and  Owen. 

There  is  every  reason  to  believe  that  the  history  of  the 
development  of  vegetation  on  any  barren  rock,  or  newly 
formed  coral  island,  illustrates  those  stages  by  which  the 
earth  itself  became  covered  with  verdure.  The  first  vege- 
table denizens  of  the  rocky  surface  in  modern  times,  are 
usually  cryptogamous  plants,  such  as  crustaceous  lichens, 
these  are  succeeded  by  the  foliaceous  species,  and  by  such 
mosses  as  Polytrichum  commune,  Hedwigia  ciliata,  and  the 
different  varieties  of  Leskia  and  Hypnum,  plants  which  are 
of  very  humble  growth,  and  of  exceedingly  simple  structure, 
consisting,  comparatively  speaking,  of  only  a  few  cells. 
The  oxalic  acid  contained  in  the  thalli  of  the  lichens,  to- 
gether with  the  oxygen  of  the  atmosphere,  slowly  disin- 
tegrate the  rocky  surface,  and  successive  generations  of 
these  lowly  protophytes  finally  create  a  humus  which  gives 
birth  to  a  more  highly  organized  vegetation.  The  higher 
cryptogamia  now  make  their  appearance,  Polypodium  vul- 
gare,  Asplenium  trichomanes,  Asplenium  ebeneum,  together 
with  the  Saxifrages,  Arenarias,  Aquilegia  Canadensis  and 
other  phanerogamous  plants.  Such  appears  to  be  the  order 
of  nature — the  cellular  Cryptogamia  preparing  the  way  for 
ferns  and  flowering  plants — the  simple  preceding  the  com- 
plex. 

That  cryptogamous  plants  are  the  most  ancient  inhabi- 
tants of  the  earth ;  that  they  existed  anterior  to  the  Pha- 


OF  PLANTS  AND  ANIMALS.  171 

nerogamia,  and  formed  for  a  long  succession  of  ages  a  lead- 
ing feature  in  the  flora  of  the  antediluvian  world,  is  evident, 
if  we  consult  the  pages  of  geological  history.  It  is  true 
that  the  cellular  Cryptogamia,  such  as  lichens  and  mosses, 
are  very  seldom  found  in  a  fossil  state ;  but  this  is  not  to 
be  wondered  at,  when  we  remember  that  the  preservation 
of  plants  in  this  condition  necessarily  depends  on  their 
structure.  The  fossil  Cryptogamia,  which  have  a  woody 
and  vascular  structure,  have  however,  been  preserved  in 
the  greatest  abundance. 

The  absence  of  organic  remains  in  rocks  is  not  always 
sufficient  to  enable  us  to  state  that  these  rocks  were  formed 
before  animals  or  vegetables  existed,  since  the  late  Prof. 
Forbes  has  shown  that,  even  in  the  present  day,  there  are 
depths  in  the  ocean  which  are  destitute  of  organic  life. 
Hence  rocks  deposited  at  such  depths  might  contain  no 
organic  remains. 

Fossil  plants  are  found  in  the  aqueous  and  stratified  for- 
mations, which  have  been  divided  into  three  great  groups, 
the  Paleozoic,  the  Secondary,  and  the  Tertiary.  The  Paleo- 
zoic rocks  include  the  Silurian,  Cambrian,  and  Old  Red 
Sandstone  and  Carboniferous  formations.  In  the  Silurian, 
Cambrian,  and  Old  Red  Sandstone  we  meet  with  the  remains 
of  marine  plants,  and  also  a  few  terrestrial  species.  In  the 
Old  Red  Sandstone  of  Scotland,  Miller  has  detected  fucoid 
ferns,  and  in  the  same  formation  at  Oporto,  Bunbury  has 
found  Pecopteris  cyathea,  P.  muricata,  and  Neuropteris 
tenuifolia,  ferns  which  are  closely  allied  to  those  of  the  car- 
boniferous period.  There  was  land,  therefore,  as  well  as 
water  at  this  remote  epoch,  although  the  abundance  of  fishes 
and  marine  plants  seems  to  indicate  that  the  sea  covered 
the  greater  part  of  the  earth's  surface. 

Towards  the  close  of  the  paleozoic  period,  however,  land 


172  THE  GEOLOGICAL  SUCCESSION 

plants  appear  to  have  been  developed  on  an  enlarged  scale. 
Coal  owes  its  origin  to  the  abundant  vegetation  of  this 
era;  for  it  is  now  universally  admitted  that  this  substance 
is  of  vegetable  origin.  This  the  microscope  has  fully  de- 
monstrated. In  some  kinds  of  coal,  punctuated  woody  fibre 
has  been  detected,  in  others  dotted  and  scalariform  tissue, 
as  well  as  cells  of  various  kinds.  The  occurrence  of  dotted 
and  scalariform  vessels  indicates  the  presence  of  ferns  and 
their  allied  forms,  such,  as  Sigillaria,  Stigmaria  and  Lepi- 
dodendra,  whilst  true  punctuated  wood  implies  the  pre- 
sence of  Coniferae. 

Impressions  of  these  plants  are  abundant  amongst  the 
argillaceous  and  sandy  beds  of  the  carboniferous  system. 
About  one  hundred  and  fifty  species  of  fossil  ferns  have 
been  distinguished  by  Botanists  in  the  coal  system  of  Eng- 
land, and  many  of  the  fronds  of  these  ferns  have  been 
clearly  ascertained  to  have  fallen  from  the  stems  of  tree- 
ferns,  which  grew  at  the  time  that  the  coal  was  deposited. 
The  Lepidodendrons  were  gigantic  Lycopodiums,  or  club 
mosses,  which  rose  to  the  height  of  sixty  feet,  although  the 
representatives  of  these  plants  are  now  mere  herbs. 

In  the  Secondary  formations  we  meet  with  a  greater  num- 
ber of  Coniferse  and  Cicadacese,  whilst  ferns  and  Lycopo- 
diacese  are  not  so  abundant,  and  less  gigantic  in  their 
growth. 

The  Tertiary  period  is  characterized  by  an  abundance  of 
Dicotyledonous  and  Monocotyledonous  plants,  especially 
palms. 

Many  of  the  fossil  plants  of  these  deposits,  such  as  pines, 
elms,  beeches,  and  maples,  may  be  referred  to  genera  at 
present  existing,  and  merely  present  specific  differences. 
The  general  result  of  all  researches  in  fossil  botany  tends 
to  prove  that  the  early  vegetation  of  the  globe  consisted  of 


OF  PLANTS  AND  ANIMALS.  173 

plants  of  extreme  simplicity  of  organization.  The  more 
ancient  the  geological  formation  the  greater  is  the  differ- 
ence between  its  fossil  plants  and  those  now  living;  whilst 
on  the  other  hand,  the  Tertiary  deposits  which  are,  com- 
paratively speaking,  recent  in  the  history  of  creation,  con- 
tain in  addition  to  species  now  extinct,  botanical  remains 
which  are  identical  with  species  now  living.  There  has 
therefore  been  a  gradual  approximation  of  vegetation  to  its 
present  condition. 

There  appears  to  have  been  a  similar  progression  in  the 
animal  creation.  All  naturalists  admit  that  the  animal  re- 
mains found  in  the  Primary  or  Paleozoic  rocks  are  charac- 
terized by  great  simplicity  of  organization,  and  that  the 
animals  of  this  period  present  the  least  resemblance  to  those 
now  living.  The  articulata  are  mostly  trilobites — animals 
which  evidently  belong  to  the  lower  order  of  the  Crus- 
taceans. There  is  an  incompleteness  and  want  of  develop- 
ment in  the  form  of  their  body,  that  strongly  reminds  us 
of  the  embryo  among  the  crabs.  The  class  of  insects  is 
entirely  wanting.  The  radiata  are  represented  by  the  Crino- 
idea,  or  lily-like  zoophytes,  animals  remarkable  for  the  sim- 
plicity of  their  organization,  and  the  peculiarly  complicated 
structure  of  their  skeleton.  The  body  of  these  Crinoids 
was  supported  on  a  long  and  flexible  column,  which  was 
attached  to  a  rock  or  some  other  hard  substance,  at  the* 
bottom  of  the  sea.  This  column  was  composed  of  an  im- 
mense number  of  joints,  through  which  an  aperture  de- 
scended from  the  stomach  to  the  base  or  support.  The 
bodies  of  the  Crinoidea,  like  that  of  the  Hydra,  were  sim- 
ple digestive  cavities  surrounded  with  jointed  tentaculse  of 
the  same  structure  as  the  stem,  which  the  animal  had  the 
power  of  spreading  abroad  for  the  purpose  of  grasping  its 
prey.  These  animals  belonged  to  the  class  of  Echinoderms, 
15* 


174         T^HE  GEOLOGICAL  SUCCESSION 

represented  at  present  by  the  star  fishes  and  sea-urchins,  a 
far  more  highly  organized  race.  Numerous  brachiopod 
molluscs,  the  lowest  of  the  class,  have  been  discovered  in 
the  Paleozoic  rocks.  The  class  of  worms  is  represented  by 
a  few  serpulse.  But  the  most  convincing  proof  of  the 
organic  inferiority  of  the  first  animal  inhabitants  of  our 
globe  is  afforded  by  the  remains  of  the  fossil  vcrtebrata  of 
this  epoch  which  are  those  of  a  low  order  of  fishes.  These 
were  then  the  most  highly  organized  animals.  Hence  the 
period  has  been  called  by  Agassiz,  the  AGE  or  FISHES. 
There  was  as  yet  neither  reptiles,  birds,  nor  mammals. 
The  sea  appears  to  have  covered  the  greater  portion  of  the 
earth — an  ocean  without,  a  shore.  The  animals  were  all 
aquatic,  and  the  vegetation  marine;  and  " among  the  aqua- 
tic population  no  sound  was  heard.  All  creation  was  then 
silent/7* 

Towards  the  close  of  the  paleozoic  period,  the  earth  ap- 
pears to  have  presented  the  aspect  of  a  vast  ocean  studded 
with  an  immense  number  of  islands,  which  were  covered 
with  a  luxuriant  vegetation,  consisting  principally  of  arbor- 
escent ferns,  Equisetacese,  Calamites,  Lycopodiacese,  and 
Coniferae — plants  of  very  simple  structure,  but  of  gigantic 
size.  It  was  during  this  geological  era  that  the  coal  was 
deposited. 

The  animals  of  the  carboniferous  formation  resemble,  in 
many  respects,  those  of  the  paleozoic  epoch.  The  crus- 
taceans, however,  have  evidently  improved.  In  addition 
to  the  trilobites,  we  have  the  horse-shoe  crabs,  and  other 
gigantic  forms.  We  also  meet  with  traces  of  insects  and 
scorpions.  We  come  now  to  that  immense  period  in  the 
natural  history  of  the  earth,  which  geologists  have  called 

The  Secondary  Age,  or  the  AGE  OF  REPTILES.     The 

*  Louis  Agassiz. 


OF  PLANTS  AND  ANIMALS.  175 

carboniferous  rocks  have  been  included  within  the  geologi- 
cal formations  of  this  period  by  some  geologists,  because 
they  contain  the  remains  of  the  first  land  animals ;  whereas 
in  the  paleozoic  age,  the  animals  were  altogether  marine, 
breathing  by  gills.  Reptiles,  however,  are  not  found  in 
the  coal  measures,  and  do  not  make  their  appearance  until 
about  the  time  of  the  deposition  of  the  New  Red  Sandstone, 
which  took  place  immediately  after  the  formation  of  the 
carboniferous  rocks.  The  tracks  of  a  gigantic  Batrachian 
animal,  a  creature  allied  to  the  frog,  have  been  left  on  the 
New  Red  Sandstone  of  Pennsylvania  and  Germany ;  enor- 
mous aquatic  birds  have  also  left  the  impression  of  their 
footsteps  on  the  same  rocks  in  Connecticut. 

The  reptiles  seem  to  have  attained  their  maximum  de- 
velopment during  the  Oolitic  period.  We  find  in  this  for- 
mation those  enormous  amphibia  known  by  the  names 
Ichthyosaurus,  Plesiosaurus,  Megalosaurus  and  Iguanodon, 
animals  somewhat  allied  to  the  lizard  and  crocodile  in 
structure.  But  the  most  wonderful  relic  of  the  age  of 
reptiles,  is  the  Pterodactylus,  which  resembled  a  gigantic 
bat,  and  is  thought  to  have  been  capable  of  flying.  The 
trilobites  are  now  extinct ;  but  in  the  upper  stages  of  the 
Oolitic,  we  meet  with  tortoises  and  also  the  impressions  of 
several  families  of  insects,  among  which  dragon  flies  and 
beetles  are  conspicuous. 

All  the  invertebrated  animals,  including  the  mollusca, 
the  articulata,  and  the  radiata,  are  largely  represented.  The 
peculiar  forms  of  the  paleozoic  age  have  nearly  all  disap- 
peared, and  are  replaced  by  creatures  whose  organization 
is  adapted  to  the  new  conditions.  Of  the  brachiopod  mol- 
luscs, only  one  type  is  abundant,  that  of  the  Terebratula. 
The  G-asteropods  display  a  great  variety  of  species,  and  also 
the  Cephalopods,  among  which  the  Ammonites  are  the 


176  THE  GEOLOGICAL  SUCCESSION 

most  prominent.  The  Belemnites  also  abound,  creatures 
resembling  the  cuttle  fish.  The  polyparia  were  very  abun- 
dant in  the  seas  of  the  Oolitic  period.  Whole  rocks  are 
entirely  formed  out  of  the  remains  of  these  animals.  The 
crinoids  are  not  quite  so  numerous  as  in  former  ages;  but 
star-fishes  abound,  and  an  extraordinary  and  beautiful  va- 
riety of  sea  urchin  with  large  spines,  the  Cidaris  coronata. 
The  animals  of  the  Cretaceous  period  bear  the  same  gene- 
ral characters  as  those  of  the  Oolitic,  but  with  a  more 
marked  tendency  towards  existing  forms.  It  is  true  that 
there  is  some  evidence  of  the  existence  of  mammalia,  but 
they  are  few  and  insignificant.  The  only  traces  of  mam- 
malia consist  of  two  or  three  marsupial  animals — creatures 
allied  to  the  opossum.  Throughout  the  whole  of  this  im- 
mense period  of  time,  the  class  reptilia  was  the  preponde- 
rating form.  The  lower  forms  of  both  animal  and  vege- 
table life  attained  a  gigantic  development.  "  With  flocks  of 
pterodactyles  flying  in  the  air,  and  shoals  of  no  less  mon- 
strous ichthyosauri  and  plesiosauri  swarming  in  the  ocean, 
and  gigantic  crocodiles  and  tortoises  crawling  on  the  shores 
of  the  primeval  lakes  and  rivers ;  air,  sea,  and  land  must 
have  been  strangely  tenanted  in  these  early  periods  of  our 
infant  world/'* 

In  those  geological  periods  immediately  following  the 
deposition  of  the  chalk,  the  last  formation  of  the  secondary 
age,  the  marine  or  amphibian  reptiles  are  replaced  by  nu- 
merous mamm/dia  of  enormous  size.  These  periods  com- 
prise the  different  tertiary  formations.  This  era  has, 
therefore,  been  called  the  AGE  or  MAMMALS.  The  animal 
remains  contained  in  these  formations,  strikingly  approxi- 
mate in  organic  development  to  the  species  now  living. 

«  Dr.  Buckland. 


OP  PLANTS  AND  ANIMALS.  177 

Many  of  the  animals  peculiar  to  former  eras  have  passed 
away.  The  two  great  families  of  Ammonites  and  Belem- 
nites  are  no  more.  A  multitude  of  species  of  molluscs  are 
however  found,  which  more  or  less  resemble  those  of  the 
present  era,  some  of  them  being  in  fact  identical  with  those 
in  the  adjacent  seas. 

The  most  ancient  of  the  tertiary  deposits  is  characterized 
by  the  presence  of  great  pachyderms,  or  thick-skinned  ani- 
mals, among  which  we  may  mention  the  Paleotherium  and 
Anoplotherium,  creatures  which  approached  the  rhinoceros 
and  tapir  in  the  peculiarities  of  their  organization.  These 
fossil  mammalia  were  first  found  in  the  gypsum  beds  of  the 
Paris  basin.  Their  bones  were  brought  to  Cuvier,  who 
re-constructed  them,  and  thus  laid  the  foundations  of  the 
science  of  Paleontology.  In  these  ancient  tertiary  deposits 
the  earliest  remains  of  monkeys  have  also  been  detected. 

The  animals  of  the  most  recent  tertiary  formations  re- 
semble, still  more  closely,  those  of  the  present  epoch.  The 
fossil  remains  represent  all  the  terrestrial  and  aquatic  spe- 
cies now  living  around  us,  and  besides  these,  many -types 
now  extinct,  some  of  them  of  monstrous  size,  such  as  the 
mastodon,  or  fossil  elephant,  which  is  probably  the  last 
large  animal  which  became  extinct  prior  to  the  creation  of 
man. 

By  these  revolutions  of  organic  and  inorganic  nature 
was  the  world  finally  fitted  for  the  abode  of  man.  In  the 
tertiary  formations,  which  preceded  the  AGE  OF  MAN,  no 
human  remains  have  been  discovered,  no  skeletons  except 
those  of  the  hitherto  irrational  denizens  of  the  earth.  Man 
is,  therefore,  comparatively  speaking,  a  recent  creation. 

If  we  consider  the  men  of  the  earliest  time  as  children 
in  intellectual  capacity,  gradually  advancing  from  a  state 
of  the  most  brutal  ignorance,  to  a  clear  and  rational  per- 


178  THE  GEOLOGICAL  SUCCESSION 

ception  of  their  own  capabilities,  and  their  power  of  under- 
standing and  controlling  nature,  we  shall  probably  enter- 
tain an  opinion  which  approximates  to  the  truth. 

Whilst  an  untutored  savage,  man  must  have  lived  on  the 
spontaneous  -productions  of  the  earth  which  he  was  unable 
at  this  period  of  his  history  to  cultivate.  Slowly  did  he 
arrive  at  a  consciousness  of  his  power  over  the  other  ani- 
mals, which  at  first  disputed  his  dominion,  but  ultimately 
fled  before  him.  This-  stimulated  pursuit.  He  became 
a  hunter;  especially  as  he  found  the  skins  of  the  wild 
inhabitant  of  the  woods  useful  as  an  article  of  clothing,  and 
the  flesh  of  some  of  them  nutritious.  He  chose  for  his 
dwelling  the  margin  of  rivers  and  lakes,  or  the  sea  shore, 
whose  banks  were  more  or  less  covered  with  plants,  and 
whose  waters  abounded  in  fish.  These  he  sought  by  force 
or  craft  to  obtain. 

Even  now  the  red  Indians,  in  those  portions  of  this  con- 
tinent yet  uncivilized,  subsist  in  this  manner;  and  such 
appears  to  have  been  originally  the  condition  of  the  ances- 
tors of  all  civilized  nations. 

To  avoid  the  trouble  of  hunting  perpetually,  such  ani- 
mals as  he  found  useful  for  the  supply  of  his  wants,  he 
endeavored  to  tame  them.  But  the  animals  most  readily 
subjugated  were  ruminants  or  plant-eaters,  for  which  pas- 
ture ground  must  be  provided.  As  a  herdsman  with 
his  flock,  from  one  place  to  another,  he  now  wandered, 
dwelling  in  huts,  until  experience  finally  taught  him  to 
select  those  spots  which  produced  the  plants  most  useful 
for  his  animals,  and  sufficient  in  quantity  to  give  them 
continuous  support. 

He  now  erected  for  himself  settled  habitations,  and  re- 
sorted to  stones  and  metals  to  give  them  greater  durability 
and  strength.  United  he  put  forth  mightier  efforts,  he 


OP  PLANTS  AND  ANIMALS.  179 

built  cities  and  founded  empires.  We  have  arrived  now  at 
the  historical  era.  From  the  written  accounts  which  have 
been  transmitted  to  us,  it  is  clear  that  the  long  reign  of 
instinct  is  giving  place  to  that  of  reason,  and  that  the  pre- 
sent period  of  the  world's  history  is  characterized  by  its 
slow  development. 

The  occurrence  of  human  skeletons,  and  of  coins  and 
works  of  art,  in  modern  fluviatile  and  marine  deposits ;  the 
preservation  of  the  bones  of  the  existing  species  of  ani- 
mals, and  of  the  leaves  and  branches  of  plants  now  grow- 
ing on  the  earth's  surface,  in  the  various  geological  forma- 
tions now  in  progress,  shows  the  immutability  of  nature, 
and  proves  that  the  same  enduring  monuments  of  the  pre- 
sent state  of  things  will  be  transmitted  to  future  ages. 
When  the  beds  now  forming  in  the  existing  seas  shall  be 
elevated  above  the  waters  and  covered  with  woods  and 
forests;  when  the  deltas  of  our  rivers  shall  be  converted 
into  fertile  tracts,  and  become  the  sites  of  towns  and  cities ; 
in  excavating  the  earth  thus  newly  created,  there  is  little 
doubt  that  the  then  existing  races  of  men  will  discover  the 
same  indelible  records  of  the  physical  history  of  our  times, 
as  we  have  now  of  that  of  former  ages. 

The  Linnsean  maxim,  "Natures  mirandaest  maxime  in 
minimis,"  nature  is  chiefly  to  be  admired  in  the  least 
things,  is  as  yet  only  partially  appreciated  by  a  few  distin- 
guished minds,  although  it  should  never  be  lost  sight  of 
in  the  investigation  of  vital  phenomena.  If  it  be  philoso- 
phical to  pursue  researches  in  the  physical  sciences  by  ex- 
periments and  observations  on  the  properties  of  inorganic 
matter ;  it  would  seem  to  be  equally  in  accordance  with  the 
principles  of  science,  in  the  study  of  organic  nature,  to 
adhere  as  closely  as  possible  to  the  plan  of  nature,  and 
trace  her  operations  in  the  simpler  forms  of  life  before  we 


180  THE  GEOLOGICAL  SUCCESSION,  ETC. 

attempt  the  study  of  those  that  are  more  complicated.  The 
development  of  the  simple  before  the  complex,  appears  to 
have  ever  been  the  plan  of  nature,  whether  her  operations 
be  traced  in  time  or  through  the  dark  geological  periods  of 
the  past;  and  whether  we  contemplate  the  successive  phases 
through  which  life  has  already  passed,  or  the  organic  phe- 
nomena of  the  present  living  races  of  plants  and  animals, 
we  see  everywhere  evidence  of  the  immutability  of  nature, 
and  the  uniformity  of  her  organic  laws. 


THE   END. 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

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